CN111450667B - Separation method and apparatus for light inert gas - Google Patents
Separation method and apparatus for light inert gas Download PDFInfo
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- CN111450667B CN111450667B CN201910315963.3A CN201910315963A CN111450667B CN 111450667 B CN111450667 B CN 111450667B CN 201910315963 A CN201910315963 A CN 201910315963A CN 111450667 B CN111450667 B CN 111450667B
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
- B01D53/228—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion characterised by specific membranes
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- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
- B01D53/04—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with stationary adsorbents
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- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
- B01D53/04—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with stationary adsorbents
- B01D53/0454—Controlling adsorption
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- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
- B01D53/04—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with stationary adsorbents
- B01D53/047—Pressure swing adsorption
- B01D53/0476—Vacuum pressure swing adsorption
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- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B23/00—Noble gases; Compounds thereof
- C01B23/001—Purification or separation processes of noble gases
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- C01B23/0042—Physical processing only by making use of membranes
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- C01B23/00—Noble gases; Compounds thereof
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- C01B2210/00—Purification or separation of specific gases
- C01B2210/0029—Obtaining noble gases
- C01B2210/0031—Helium
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- C01—INORGANIC CHEMISTRY
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- C01B2210/00—Purification or separation of specific gases
- C01B2210/0029—Obtaining noble gases
- C01B2210/0032—Neon
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- C01—INORGANIC CHEMISTRY
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- C01B2210/00—Purification or separation of specific gases
- C01B2210/0029—Obtaining noble gases
- C01B2210/0034—Argon
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Abstract
A method and apparatus for producing a helium, neon or argon product gas using an adsorptive separation unit having a minimum dead end volume. The purification unit receives a helium, neon or argon rich stream and the stream is recycled from the purification unit back to the adsorptive separation unit in a controlled manner to maintain the concentration of helium, neon or argon in the feed to the separation unit within a target range.
Description
Cross reference to related applications
This application is a continuation-in-part application of U.S. patent application No.15/850,646 filed on 21.12.2017, which is incorporated herein by reference in its entirety, and claims priority thereto.
Background
The present disclosure relates to the recovery of light inert gas from a gas mixture containing the light inert gas and at least one other component. The light inert gas may be helium, neon or argon.
Various methods and techniques have been developed to separate and recover light inert gases from multi-component gas streams. These methods include stand-alone membrane separation units, stand-alone adsorption units, stand-alone cryogenic units, and combinations of membrane separation units, cryogenic units, and Pressure Swing Adsorption (PSA) units. As used herein, the term "pressure swing adsorption" includes "vacuum pressure swing adsorption" and "vacuum pressure swing adsorption".
Disclosures relating to such methods and/or techniques include WO 2016/096104; DE 102007022963; and U.S. Pat. No.3,250,080; 3,324,626, respectively; 4,077,779, respectively; 4,690,695; 4,701,187, respectively; 4,717,407, respectively; 4,783,203, respectively; 5,542,966, respectively; 8,152,898, respectively; 8,268,047, respectively; and US app.pub.no. 2017/0312682; and US publication nos. 16/102,936 and 16/103,569, both filed 8/14/2018.
It is desirable in the industry to recover light inert gases from various feed streams containing the desired light inert gases.
For example, it is desirable to recover helium from a feed stream (e.g., natural gas) having a low helium concentration, such as 0.1 to 4 mole% or 0.1 to 2 mole% helium, or 0.1 to 1 mole% helium. Other example feed streams include a nitrogen bleed unit (NRU) exhaust stream, a gas stream vaporized or flashed from a liquefied natural gas process, CO2A liquefied exhaust stream, a recycle stream during manufacturing, a recovery stream during airship filling, a vent in an air separation unit where a reboiler is not condensable, high pressure gaseous nitrogen (HPGAN) from an air separation unit, reflux to a low pressure column in an air separation unit, or a liquefied nitrogen storage tank vent.
It is desirable in the industry to recover light inert gases from a feed stream whose concentration of light inert gas varies over time.
It is also desirable in the industry to produce a product gas containing light inert gas that is suitable for use with feed streams having varying concentrations of light inert gas within target concentration specifications.
Summary of The Invention
The present invention relates to a method and an apparatus for separating light inert gas from a feed gas stream comprising light inert gas and at least one other component.
There are several aspects of the invention as summarized below. In the following, reference numerals and expressions provided in parentheses refer to example embodiments explained further below with reference to the drawings. However, the reference numbers and expressions are merely illustrative and do not limit the aspect to any particular components or features of the example embodiments. The components and features of any embodiment may be combined with one or more components or features from one or more other embodiments, and all such combinations are contemplated to be within the scope of the present invention. These aspects may be expressed as claims, in which reference signs and expressions placed between parentheses are omitted or denoted otherwise as appropriate.
Aspect 1. an apparatus for producing a light inert gas-enriched product stream (25) from a feed gas (11), the feed gas comprising a light inert gas and at least one other gas component, the light inert gas selected from the group consisting of helium and neon, the apparatus comprising:
an adsorption separation unit (10), wherein the adsorption separation unit (10) comprises:
a plurality of vessels (100a, 100b, 100c, 100d, 100e), each containing a bed of adsorbent;
a feed gas header (200) in selective fluid communication with each of the plurality of vessels (100a, 100b, 100c, 100d, 100 e);
a product gas header (210) in selective fluid communication with each of the plurality of vessels (100a, 100b, 100c, 100d, 100 e);
an off-gas header (220) in selective fluid communication with each of the plurality of vessels (100a, 100b, 100c, 100d, 100 e);
a process gas delivery line operatively connecting the plurality of vessels (100a, 100b, 100c, 100d, 100e) to the feed gas header (200), the product gas header (210), and the off-gas header (220);
each vessel (100) of the plurality of vessels (100a, 100b, 100c, 100d, 100e) having a process gas delivery line (101, 102, 103, 104, 105, 106, 107, 108) associated therewith;
a plurality of valves in the process gas delivery line, including a plurality of valves (110, 111, 112, 113, 114, 115) adjacent to and associated with each respective vessel (100);
wherein the adsorption separation unit (10) has a corresponding one to eachThe central volume V of the process gas delivery lines (101, 102, 103, 104, 105, 106, 107, 108) associated with the container (100)c；
Wherein the central volume of each respective container is the sum of:
(i) a volume contained in a process gas delivery line (110, 111, 112, 113, 114, 115) associated with a respective vessel (100), each valve connecting the respective vessel to the vicinity of the respective vessel,
(ii) all dead end volumes (109), if any, are connected to the respective containers (100) at junctions, and
(iii) all dead-end volumes, if any, are connected at junctions to any process gas delivery lines associated with a respective vessel (100), connecting the respective vessel (100) to any valve (110, 111, 112, 113, 114, 115) adjacent to the respective vessel (100);
wherein the central volume of each respective container comprises a second volume V2Wherein the second volume is the sum of:
(i) all dead-end volumes (109), if any, are connected to respective containers (100);
(ii) all volumes of dead end volume, if any, are connected at a junction to any process gas delivery line associated with a respective vessel (100), connecting the respective vessel (100) to any valve (110, 111, 112, 113, 114, 115) adjacent to the respective vessel (100); and
(iii) a volume (108) of any process gas delivery lines, if any, having a first end terminating in a valve (115) adjacent to the respective vessel (100) configured to allow process gas to be transferred to an off-gas header (220) when opened, and having a second end terminating at a junction in any other associated process gas delivery line (102), connecting the respective vessel (100) to any other valve (110) adjacent to the respective vessel (100); and
wherein the second volume V2Less than the central volume V of each container (100)cOr less than 3%, or less than 1%.
a purification unit (20), the purification unit (20) having an inlet, a first outlet and a second outlet, the inlet being in fluid communication with a product gas header (210) of the adsorptive separation unit (10);
the gas mixer (60) having a first inlet for receiving a flow of the feed gas (11), a second inlet in fluid communication with a second gas source (17) having a higher concentration of light inert gas than the feed gas (11), wherein the feed gas header (200) of the adsorptive separation unit (10) is in downstream fluid communication with the outlet of the gas mixer (60);
a sensor (50) in at least one of: (i) a feed gas line (11) supplying a first inlet of the gas mixer (60); (ii) a process gas delivery line (12) connecting the outlet of the gas mixer (60) to the feed gas header (200) of the adsorption separation unit (10); and (iii) a feed gas header (200); and
a controller (80) in signal communication with the sensor (50), the controller (80) operable to control a flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) r in response to a signal from the sensor (50).
A feed membrane separation unit (85) having an inlet for receiving a feed gas stream (11), a permeate outlet and a non-permeate outlet;
an adsorption separation unit (10), wherein the adsorption separation unit (10) comprises:
a plurality of vessels (100a, 100b, 100c, 100d, 100e), each containing a bed of adsorbent;
a feed gas header (200) in selective fluid communication with each of the plurality of vessels (100a, 100b, 100c, 100d, 100 e);
a product gas header (210), each of the plurality of vessels (100a, 100b, 100c, 100d, 100e) being in selective fluid communication;
an off-gas header (220) in selective fluid communication with each of the plurality of vessels (100a, 100b, 100c, 100d, 100 e);
a process gas delivery line operatively connecting the plurality of vessels (100a, 100b, 100c, 100d, 100e) to the feed gas header (200), the product gas header (210), and the off-gas header (220);
each vessel (100) of the plurality of vessels (100a, 100b, 100c, 100d, 100e) having a process gas delivery line (101, 102, 103, 104, 105, 106, 107, 108) associated therewith;
a plurality of valves in the process gas delivery line, including a plurality of valves (110, 111, 112, 113, 114, 115) adjacent to and associated with each respective vessel (100);
wherein the adsorption separation unit (10) has a central volume V of the process gas delivery line (101, 102, 103, 104, 105, 106, 107, 108) associated with each respective vessel (100)c；
Wherein the central volume of each respective container is the sum of:
(i) the volume contained in the process gas delivery line associated with the respective container, each valve (110, 111, 112, 113, 114, 115) connecting the respective container to the vicinity of said respective container (100),
(ii) all dead end volumes (109), if any, are connected to the respective containers (100) at junctions, and
(iii) all dead-end volumes, if any, are connected at junctions to any process gas delivery lines associated with the respective vessel (100), connecting the respective vessel (100) to any valve (110, 111, 112, 113, 114, 115) adjacent to the respective vessel (100);
wherein the central volume of each respective container comprises a second volume V2Wherein the second volume is the sum of:
(i) all dead-end volumes (109), if any, are connected to respective containers (100);
(ii) all volumes of dead end volume, if any, are connected at a junction to any process gas delivery line associated with a respective vessel (100), connecting the respective vessel (100) to any valve (110, 111, 112, 113, 114, 115) adjacent to the respective vessel (100); and
(iii) a volume (108) of any process gas delivery lines, if any, having a first end terminating in a valve (115) adjacent to the respective vessel (100) configured to allow process gas to be transferred to an off-gas header (220) when opened, and having a second end terminating at a junction in any other associated process gas delivery line (102), connecting the respective vessel (100) to any other valve (110) adjacent to the respective vessel (100); and
wherein the second volume V2Less than the central volume V of each container (100)c5%, or less than 3%, or less than 1%; and
a conduit system for transferring a permeate stream (41) from a permeate outlet to a feed gas header of the adsorptive separation unit.
a purification unit (20), the purification unit (20) having an inlet, a first outlet and a second outlet, the inlet being in fluid communication with a product gas header (210) of the adsorptive separation unit (10);
wherein the conduit system comprises a gas mixer (60) having a first inlet for receiving said permeate stream (41), a second inlet in fluid communication with a second gas source (17) having a higher concentration of light inert gas than the permeate gas (41), and an outlet in fluid communication with the combined gas stream (12),
wherein the feed gas header (200) of the adsorption separation unit (10) is in downstream fluid communication with the outlet of the gas mixer (60);
a sensor (50) in at least one of: (i) a feed gas line (11) supplying an inlet of the feed membrane separation unit (85); (ii) a permeate stream line (41) connecting the permeate outlet of the feed membrane separation unit to the first inlet of the gas mixer (60); (iii) a combined gas flow line (12) connecting the outlet of the gas mixer (60) to the feed gas header (200) of the adsorptive separation unit (10); and (iv) a feed gas header (200); and
a controller (80) in signal communication with the sensor (50), the controller (80) operable to control a flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) in response to a signal from the sensor (50).
Aspect 7 the apparatus of aspect 6, further comprising:
a flow regulator (27) operatively disposed between the second inlet of the gas mixer (60) and the first outlet of the purification unit (20) and in signal communication with the controller (80);
wherein the controller (80) is operable to control the flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting a flow regulator (27) operatively disposed between the second inlet of the gas mixer (60) and the first outlet of the purification unit (20).
Aspect 8. the apparatus according to any one of aspects 2 or 4 to 7, wherein the second gas source (17) comprises a second outlet of the purification unit (20).
Aspect 9 the apparatus according to aspect 8, further comprising:
a flow regulator (29) operatively disposed between the second inlet of the gas mixer (60) and the second outlet of the purification unit (20) and in signal communication with the controller (80);
wherein the controller (80) is operable to control the flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting a flow regulator (29) operatively disposed between the second inlet of the gas mixer (60) and the second outlet of the purification unit (20).
wherein the second gas source (17) comprises a process gas delivery line (36) operatively connecting the product gas header (210) to an inlet of the purification unit (20).
a flow regulator (33) operatively disposed between the second inlet of the gas mixer (60) and a process gas delivery line (36), the process gas delivery line (36) operatively connecting the product gas header (210) of the adsorption separation unit (10) to the inlet of the purification unit (20) and in signal communication with the controller (80);
wherein the controller (80) is operable to control the flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting a flow regulator (33), the flow regulator (33) being operatively disposed between the second inlet of the gas mixer (60) and a process gas delivery line (36), the process gas delivery line (36) operatively connecting a product gas header (210) of the adsorptive separation unit (10) to the inlet of the purification unit (20).
wherein the gas mixer (60) has a third inlet in fluid communication with the second outlet of the purification unit (20).
a flow regulator (31) operatively disposed between the third inlet of the gas mixer (60) and the second outlet of the purification unit (20) and in signal communication with the controller (80);
wherein the controller (80) is operable to adjust a flow regulator (31) operatively disposed between the third inlet of the gas mixer (60) and the second outlet of the purification unit (20) in response to a signal from the sensor (50).
wherein the gas mixer (60) has a third inlet in fluid communication with the process gas delivery line (36) which operatively connects the product gas header (210) of the adsorptive separation unit (10) to the inlet of the purification unit (20).
Aspect 15 the apparatus of aspect 14, further comprising:
a flow regulator (37) operatively disposed between the third inlet of the gas mixer (60) and a process gas delivery line (36) and in signal communication with the controller (80), the process gas delivery line (36) operatively connecting the product gas header (210) of the adsorption separation unit (10) to the inlet of the purification unit (20);
wherein the controller (80) is operable to regulate a flow regulator (37) responsive to a signal from the sensor (50), the flow regulator (37) operatively disposed between the third inlet of the gas mixer (60) and a process gas delivery line operatively connecting a product gas header (210) of the adsorption separation unit (10) to an inlet of the purification unit (20).
wherein the second gas source (17) comprises a first outlet of the purification unit (20);
wherein the purification unit (20) comprises one or more adjustable orifices (26) in signal communication with the controller (80), the one or more adjustable orifices (26) operating to control the pressure in the purification unit (20); and
wherein the controller (80) is operable to control the flow rate of light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting the one or more adjustable orifices (26).
wherein the second gas source (17) comprises a first outlet comprising a purification unit (20);
wherein the membrane-type separation unit comprises a plurality of membrane modules and one or more control valves controlling portions of the membrane modules in operation, the one or more control valves being in signal communication with a controller (80);
wherein the controller (80) is operable to control the flow rate of light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting the portion of the membrane module in operation.
a heat exchanger (40) operable to control a temperature in the purification unit, the heat exchanger in signal communication with the controller (80);
wherein the controller (80) is operable to control the flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting the heat load of the heat exchanger (40).
Aspect 19. the apparatus according to any one of aspects 2 or 4 to 15, wherein the purification unit (20) is an adsorptive separation unit,
wherein the adsorptive separation unit comprises a plurality of vessels each containing a bed of adsorbent and one or more control valves controlling the portion of the plurality of vessels in operation, the one or more control valves in signal communication with a controller (80);
wherein the second gas source comprises a first outlet of the purification unit;
wherein the controller (80) is operable to control the flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting the portion of the plurality of vessels in operation.
Aspect 20. the apparatus according to any one of aspects 2, 4 to 15 or 19, wherein the purification unit (20) is an adsorptive separation unit,
wherein the second gas source comprises a first outlet of the purification unit;
wherein the purification unit (20) comprises a feed gas header,
wherein the purification unit (20) comprises one or more adjustable orifices (32) operative to control the pressure in a feed gas header of the purification unit (20); and
wherein the controller (80) is operable to control the flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting one or more adjustable orifices (32) that operate to control the pressure in the feed gas header of the purification unit (20).
wherein the second gas source comprises a first outlet of the purification unit;
wherein the purification unit (20) comprises an off-gas header,
wherein the purification unit (20) comprises one or more adjustable orifices (27) operative to control the pressure in the exhaust gas header of said purification unit (20); and
wherein the controller (80) is operable to control the flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting one or more adjustable orifices (27) that operate to control the pressure in the exhaust gas header of the purification unit (20).
Aspect 22. the apparatus according to any one of aspects 2, 4 to 15 or 19 to 21, wherein the purification unit (20) is an adsorptive separation unit,
wherein the second gas source comprises a second outlet of the purification unit;
wherein the purification unit (20) comprises a product gas header,
wherein the purge unit (20) comprises one or more adjustable orifices (26) operative to control the pressure in the product gas header of the purge unit (20); and
wherein the controller (80) is operable to control the flow rate of light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting one or more adjustable orifices (26) that operate to control the pressure in the product gas header of the purification unit (20).
wherein the second gas source comprises a second outlet of the purification unit; and
wherein the apparatus further comprises a heat exchanger (40) operable to control the temperature in said purification unit (20), said heat exchanger (40) being in signal communication with said controller (80); and
wherein the controller (80) is operable to control the temperature in the purification unit (20) by adjusting the heat load of said heat exchanger (40) to control the flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60).
Aspect 24. the apparatus according to any one of aspects 2, 4 to 15 or 19 to 23, wherein the purification unit (20) is a rapid cycle adsorption unit.
Aspect 25 the apparatus of aspect 24, wherein the rapid cycle adsorption unit comprises one or more rotary valves.
a rotor assembly located between the first and second stator assemblies and comprising a plurality of adsorbent beds, each bed having a rotor port at either end of the bed through which gas enters or exits the bed;
the second stator assembly includes at least one feed port, at least one discharge port and a first stator plate having: at least one feed slot for directing at least one feed gas stream from the feed inlet into any one of the rotor ports aligned with the slot; at least one discharge slot for directing a flow of a discharge gas stream from any one of the rotor ports aligned with the slot to the discharge port;
the second stator assembly includes at least one product port and a second stator plate having: at least one product tank for directing at least one product gas stream to flow between the product port and any one of the rotor ports aligned with the tank; and at least one purge slot for directing a flow of at least one purge gas stream into any of the rotor ports aligned with the slot; and
the rotor assembly is rotatable relative to the first and second stator assemblies to change the mode of operation of the respective adsorbent beds by changing the rotor ports that are aligned with the slots in the first and second stator plates.
Aspect 27. the apparatus according to any one of aspects 24 to 26, wherein the rapid cycle adsorption unit comprises 6 to 9 beds, each bed comprising a bed of adsorbent.
wherein the second gas source comprises a first outlet of the purification unit (20);
wherein the purification unit comprises one or more adjustable orifices (26, 27, 32) in signal communication with the controller (80), the one or more adjustable orifices (26, 27, 32) operating to control pressure in the purification unit (20);
wherein the controller (80) is operable to control the flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting one or more adjustable orifices (26, 27, 32) that operate to control the pressure in the purification unit (20).
wherein the second gas source comprises a first outlet of the purification unit (20);
the apparatus further includes a heat exchanger (40) operable to control a temperature in the purification unit, the heat exchanger in signal communication with the controller (80);
wherein the controller (80) is operable to control the flow rate of the light inert gas from said second gas source (17) to the second inlet of the gas mixer (60) by adjusting the heat load of the heat exchanger (40).
wherein the second gas source comprises a first outlet of the purification unit (20);
wherein the purification unit (20) comprises one or more holes (20) operative to control a reflux ratio in the purification unit; and
wherein the controller (80) is operable to control the flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting the reflux ratio in the purification unit (20).
wherein the second gas source comprises a first outlet of the purification unit (20);
wherein the purification unit (20) comprises one or more orifices (20) operative to control a distillate-to-feed ratio in the purification unit; and
wherein the controller (80) is operable to control the flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting the distillate to feed ratio in the purification unit (20).
Aspect 32. the apparatus according to any one of aspects 2, 4 to 15, or 28 to 31, wherein the purification unit (20) is a distillative separation unit,
wherein the second gas source comprises a first outlet of the purification unit (20);
wherein the purification unit (20) comprises one or more orifices (20) operative to control the product to feed ratio in the purification unit; and
wherein the controller (80) is operable to control the flow rate of the light inert gas from the second gas source (17) to the second inlet of the gas mixer (60) by adjusting the distillate to feed ratio in the purification unit (20).
Aspect 33. a process for separating a feed gas stream (11) comprising light inert gas and at least one other gas component into a light inert gas-enriched product stream (25) and a light inert gas-depleted product stream (14), the light inert gas selected from the group consisting of helium, neon, and argon, the process comprising:
combining the feed gas stream (11) with a second gas stream (17) to form a combined gas stream (12), the second gas stream (17) having a higher light inert gas content than the feed gas stream (11), the second gas stream (17) having an adjusted flow rate;
separating the adsorptive separation unit feed gas stream (15) in an adsorptive separation unit (10) to produce a light inert gas rich intermediate stream (13) and a tail gas stream (51), wherein the light inert gas-lean product stream (14) comprises at least a portion of the tail gas stream (51), wherein the adsorptive separation unit feed gas stream (15) comprises at least a portion of the combined gas stream (12); and
separating a purge unit feed gas stream (21) in a purge unit (20) to produce a light inert gas-enriched product stream (25) and a light inert gas-depleted intermediate stream (23), wherein the purge unit feed gas stream (21) comprises at least a portion of the light inert gas-enriched intermediate stream (13) from the adsorptive separation unit (10);
wherein the flow rate of the light inert gas in the second gas stream (17) is controlled in response to a measure of the light inert gas content in at least one of the feed gas stream (11), the combined gas stream (12) or the adsorption separation unit feed gas stream (15).
Aspect 34. a process for separating a feed gas stream (11) comprising light inert gas and at least one other gas component into a light inert gas-enriched product stream (25) and a light inert gas-depleted product stream (14), the light inert gas selected from the group consisting of helium, neon, and argon, the process comprising:
separating the feed gas stream (11) in a feed membrane separation unit (85) to produce a permeate stream (41) and a non-permeate stream (42);
combining the permeate stream (41) with a second gas stream (17) to form a combined gas stream (12), the second gas stream (17) having a higher light inert gas content than the permeate stream (41), the second gas stream (17) having an adjusted flow rate;
separating the adsorptive separation unit feed gas stream (15) in an adsorptive separation unit (10) to produce a light inert gas rich intermediate stream (13) and a tail gas stream (51), wherein the light inert gas-lean product stream (14) comprises at least a portion of the tail gas stream (51), wherein the adsorptive separation unit feed gas stream (15) comprises at least a portion of the combined gas stream (12); and
separating a purge unit feed gas stream (21) in a purge unit (20) to produce a light inert gas-enriched product stream (25) and a light inert gas-depleted intermediate stream (23), wherein the purge unit feed gas stream (21) comprises at least a portion of the light inert gas-enriched intermediate stream (13) from the adsorptive separation unit (10);
wherein the flow rate of the light inert gas in the second gas stream (17) is controlled in response to a measure of the light inert gas content in at least one of the feed gas stream (11), the permeate stream (41), the combined gas stream (12), or the adsorption separation unit feed gas stream (15).
Aspect 35. the method according to aspects 31 to 34, wherein the adsorptive separation unit (10) comprises:
a plurality of vessels (100a, 100b, 100c, 100d, 100e), each containing a bed of adsorbent;
a feed gas header (200) in selective fluid communication with each of the plurality of vessels (100a, 100b, 100c, 100d, 100 e);
a product gas header (210) in selective fluid communication with each of the plurality of vessels (100a, 100b, 100c, 100d, 100 e);
an off-gas header (220) in selective fluid communication with each of the plurality of vessels (100a, 100b, 100c, 100d, 100 e);
a process gas delivery line operatively connecting the plurality of vessels (100a, 100b, 100c, 100d, 100e) to the feed gas header (200), the product gas header (210), and the off-gas header (220);
each vessel (100) of the plurality of vessels (100a, 100b, 100c, 100d, 100e) having a process gas delivery line (101, 102, 103, 104, 105, 106, 107, 108) associated therewith;
a plurality of valves in the process gas delivery line, including a plurality of valves (110, 111, 112, 113, 114, 115) adjacent to and associated with each respective vessel (100);
wherein the adsorption separation unit (10) has a first and a second adsorption separation unitThe central volume V of the process gas delivery lines (101, 102, 103, 104, 105, 106, 107, 108) associated with the respective containers (100)c，
Wherein the central volume of each respective container is the sum of:
(i) a volume contained in a process gas delivery line associated with a respective vessel, each valve (110, 111, 112, 113, 114, 115) connecting the respective vessel to the vicinity of the respective vessel (100),
(ii) all dead-end volumes (109), if any, are connected to respective containers (100) at junctions, known as
(iii) All dead-end volumes, if any, are connected at junctions to any process gas delivery lines associated with a respective vessel (100), connecting the respective vessel (100) to any valve (110, 111, 112, 113, 114, 115) adjacent to the respective vessel (100);
wherein the central volume of each respective container comprises a second volume V2Wherein the second volume is the sum of:
(i) all dead-end volumes (109), if any, are connected to respective containers (100);
(ii) all dead-end volume volumes, if any, are connected at junctions to any process gas delivery lines associated with the respective vessel (100), connect the respective vessel (100) to any valves (110, 111, 112, 113, 114, 115) adjacent to the respective vessel (100), and
(iii) a volume of any process gas delivery line (108), if any, having a first end terminating in a valve (115) adjacent the respective vessel (100) configured to allow process gas to be transferred to an off-gas header (220) when opened, and having a second end terminating at a junction in any other associated process gas delivery line (102), connecting the respective vessel (100) to any other valve (110) adjacent the respective vessel (100); and
wherein the second volume V2Less than the central volume V of each container (100)cOr less than 3%, or less than 1%.
Aspect 37. the method according to any one of aspects 31 to 36, wherein the purification unit (20) is an adsorption type separation unit, a membrane type separation unit, or a distillation type separation unit.
Aspect 38. the method according to any one of aspects 31 to 37,
wherein if the light inert gas content is less than a desired lower limit, the flow rate of light inert gas in the second gas stream (17) is increased; and/or
If the light inert gas content is greater than the desired upper limit, the flow rate of the light inert gas in the second gas stream (17) is reduced.
Aspect 39. the method according to any one of aspects 31 to 38, wherein the second gas stream (17) comprises a light inert gas depleted intermediate stream (23), and wherein the flow rate of light inert gas in the second stream (17) is increased or decreased by controlling the operating conditions of the purification unit (20) in response to said light inert gas content.
reducing the pressure differential between the purification unit feed gas stream (21) and the light inert gas-enriched product stream (25) to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream (23); and/or
Increasing the pressure differential between the purification unit feed gas stream (21) and the light inert gas-enriched product stream (25) to reduce the flow rate of the light inert gas in the light inert gas depleted intermediate stream (23).
Aspect 41. the method according to aspect 39 or aspect 40, wherein the purification unit (20) is a membrane-type separation unit comprising a plurality of membrane modules, and wherein controlling the operating conditions of the purification unit (20) comprises:
reducing the number of membrane modules in operation to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream (23); and/or
Increasing the number of membrane modules in operation to reduce the flow rate of the light inert gas in the light inert gas depleted intermediate stream (23).
increasing the temperature of the purification unit feed gas stream (21) to reduce the flow rate of the light inert gas depleted intermediate stream (23); and/or
The temperature of the purification unit feed gas stream (21) is reduced to increase the flow rate of the light inert gas depleted intermediate stream (23).
Aspect 43 the method according to aspect 39, wherein the purification unit (20) is an adsorptive separation unit, operating with an adsorption cycle having a cycle time, and wherein controlling the operating conditions of the purification unit (20) comprises:
increasing the cycle time of the purification unit (20) to reduce the flow rate of the light inert gas in the light inert gas depleted intermediate stream (23); and/or
The cycle time of the purification unit (20) is reduced to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream (23).
Aspect 44. the method according to aspect 39 or 43, wherein the purification unit (20) is an adsorption separation unit having a feed gas header, and wherein controlling the operating conditions of the purification unit (20) comprises:
increasing the pressure of the purge unit feed gas stream (21) in the feed gas header of the purge unit (20) to reduce the flow rate of the light inert gas depleted intermediate stream (23); and/or
Reducing the pressure of the purge unit feed gas stream (21) in the feed gas header of the purge unit (20) to increase the flow rate of the light inert gas depleted intermediate stream (23).
Aspect 45. the method according to any one of aspects 39, 43 or 44, wherein the purification unit (20) is an adsorptive separation unit having an off-gas header, and wherein controlling the operating conditions of the purification unit (20) comprises:
increasing the pressure of the light inert gas depleted intermediate stream (23) in the off-gas header of the purification unit (20) to reduce the flow rate of light inert gas in the light inert gas depleted intermediate stream (23); and/or
Reducing the pressure of the light inert gas depleted intermediate stream (23) in the off-gas header of the purification unit (20) to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream (23).
Aspect 46. the method according to any of aspects 39 or 43 to 45, wherein the purification unit (20) is an adsorptive separation unit, operating in an adsorption cycle comprising a blowdown step having a target pressure for blowdown step end, wherein a blowdown gas stream is formed during the blowdown step, wherein controlling the operating conditions of the purification unit (20) comprises:
increasing the target pressure at the end of the blowdown step to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream (23); and/or
Reducing the target pressure at the end of the blowdown step to reduce the flow rate of light inert gas in the light inert gas depleted intermediate stream (23).
Aspect 47. the method according to any one of aspects 39 or 43 to 46, wherein the purification unit (20) is an adsorptive separation unit comprising a plurality of adsorbent beds and operating in a plurality of adsorption cycles each comprising a feed step, wherein controlling the operating conditions of the purification unit (20) comprises:
simultaneously changing over the feed step to an adsorption cycle having a lesser number of adsorbent beds to increase the flow rate of light inert gas in said light inert gas depleted intermediate stream (23); and/or
Simultaneously changing over the feed step to an adsorption cycle having a greater number of adsorbent beds to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream (23).
Aspect 48. the method according to any one of aspects 39 or 43 to 47, wherein the purification unit (20) is an adsorptive separation unit comprising a plurality of adsorption beds and operating in a plurality of adsorption cycles comprising a pressure equalization step, wherein controlling the operating conditions of the purification unit (20) comprises:
altering the adsorption cycle to a lesser degree of pressure equalization by using fewer or no pressure equalization steps and/or reducing the total moles of gas delivered in one or more pressure equalization steps to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream (23); and/or
The adsorption cycle is modified to have a greater degree of pressure equalization by using a greater number of pressure equalization steps and/or increasing the total moles of gas delivered in one or more pressure equalization steps to reduce the flow rate of light inert gas in the light inert gas depleted intermediate stream (23).
Aspect 49 the method according to any one of aspects 39 or 43 to 48, wherein the purification unit (20) is an adsorptive separation unit, operating in an adsorption cycle comprising a purge step comprising a light inert gas in a light inert gas enriched intermediate stream, and controlling the operating conditions of the purification unit (20) comprises:
increasing the flow rate of the purging step to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream (23); and/or
Reducing the flow rate of the purge step to reduce the flow rate of light inert gas in the light inert gas depleted intermediate stream (23).
increasing the ratio of feed flow to product flow in the repressurization step to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream (23); and/or
The ratio of feed flow to product flow is reduced in the repressurization step to reduce the flow rate of the light inert gas depleted intermediate stream (23).
increasing the feed temperature to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream (23); and/or
The feed temperature is reduced to reduce the flow rate of the light inert gas in the light inert gas depleted intermediate stream (23).
Aspect 52. the method according to aspect 39, wherein the purification unit (20) is a distillation-type separation unit having an operating pressure, wherein controlling the operating conditions of the purification unit (20) comprises:
reducing the operating pressure of the purification unit (20) to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream (23); and/or
Increasing the operating pressure of the purification unit (20) to reduce the flow rate of the light inert gas in the light inert gas depleted intermediate stream (23).
increasing the reflux ratio of the purification unit (20) to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream (23); and/or
Reducing the reflux ratio of the purification unit (20) to reduce the flow rate of the light inert gas in the light inert gas depleted intermediate stream (23).
Aspect 54. the method according to any one of aspects 39 or 52 to 53, wherein the purification unit (20) is a distillation-type separation unit having an operating temperature, wherein controlling the operating conditions of the purification unit (20) comprises:
reducing the operating temperature of the purification unit (20) to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream (23); and/or
Increasing the operating temperature of the purification unit (20) to reduce the flow rate of the light inert gas in the light inert gas depleted intermediate stream (23).
Aspect 58. the method of aspect 57, wherein the rapid cycle adsorption unit comprises one or more rotary valves.
Aspect 59 the method of aspect 57 or 58, wherein the fast cycle adsorption unit comprises a rotor assembly and first and second stator assemblies, wherein:
said rotor assembly being located between said first and second stator assemblies and comprising a plurality of adsorbent beds, each adsorbent bed having a rotor port at either end of the bed through which gas enters or exits said bed;
the second stator assembly includes at least one feed port, at least one discharge port and a first stator plate having: at least one feed slot for directing at least one feed gas stream from the feed inlet into any one of the rotor ports aligned with the slot; at least one discharge slot for directing a flow of a discharge gas stream from any one of the rotor ports aligned with the slot to the discharge port;
the second stator assembly includes at least one product port and a second stator plate having: at least one product tank for directing at least one product gas stream to flow between the product port and any one of the rotor ports aligned with the tank; and at least one purge slot for directing a flow of at least one purge gas stream into any of the rotor ports aligned with the slot; and
the rotor assembly is rotatable relative to the first and second stator assemblies to change the mode of operation of the respective adsorbent beds by changing the rotor ports that are aligned with the slots in the first and second stator plates.
Brief Description of Drawings
FIG. 1 is a process flow diagram of a light inert gas recovery process according to the method and apparatus of the present invention.
Figure 2 is a process flow diagram of an adsorption separation unit suitable for use in the method.
FIG. 3 is a cycle diagram of a 5-bed adsorptive separation unit suitable for use in the process.
FIG. 4 is a graph of helium recovery versus% helium in the feed gas.
FIG. 5 is a graph of helium recovery versus helium content in a product stream.
FIG. 6 is a graph of helium content in the product stream as a function of atomic percent helium in the feed gas stream.
Figure 7 shows helium recovery versus% helium in a feed gas stream.
FIG. 8 is a process flow diagram of a light inert gas recovery process including a feed membrane separation unit in accordance with the method and apparatus of the present invention.
Detailed Description
The following detailed description merely provides preferred exemplary embodiments, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the ensuing detailed description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims.
The articles "a" or "an" as used herein mean one or more when applied to any feature in embodiments of the present invention described in the specification and claims. The use of "a" or "an" does not limit the meaning of individual features unless such a limitation is specifically stated. The article "the" preceding singular or plural nouns or noun phrases denotes a particular specified feature or specified particular specified features and may have a singular or plural connotation depending upon the context in which it is used.
The adjective "any" means one, some, or all, regardless of quantity.
The term "and/or" placed between a first entity and a second entity includes any meaning of (1) only the first entity, (2) only the second entity, and (3) the first entity and the second entity. The term "and/or" placed between the last two entities of a list of 3 or more entities means at least one entity in the list, including any specific combination of entities in the list. For example, "A, B and/or C" has the same meaning as "a and/or B and/or C" and includes the following combination of A, B and C: (1) a only, (2) B only, (3) C only, (4) A and B but not C, (5) A and C but not B, (6) B and C but not A, and (7) A and B and C.
The phrase "at least one of" preceding a list of features or entities refers to one or more features or entities in the list of entities, but does not necessarily include at least one of each of the entities explicitly listed in the list of entities, and does not exclude any combination of the entities in the list of entities. For example, "at least one of A, B or C" (or, equivalently, "at least one of A, B and C" or, equivalently, "at least one of A, B and/or C") has the same meaning as "a and/or B and/or C" and includes combinations of A, B and C: (1) a only, (2) B only, (3) C only, (4) A and B but not C, (5) A and C but not B, (6) B and C but not A, and (7) A and B and C.
The term "plurality" means "two or more than two".
The phrase "at least a portion" means "partially or completely". At least a portion of the stream may have the same composition, and the concentration of each species is the same, as the stream from which it is derived. At least a portion of the stream may have a species concentration that is different from the species concentration of the stream from which it is derived. At least a portion of the stream may include only the particular category of stream from which it is derived.
As used herein, a "split portion" of a stream is a portion that has the same chemical composition and concentration of a substance as the stream from which it is taken.
As used herein, a "separated portion" of a stream is a portion having a different chemical composition and different concentration of a substance than the stream it employs. The separation section may be, for example, a section formed by separation in a separator.
The term "portion" includes "separate portions" and "isolated portions".
As used herein, "first," "second," "third," and the like are used to distinguish between various steps and/or features, and do not denote a total number or relative position in time and/or space, unless expressly stated otherwise.
The term "depleted" or "lean" refers to having a lower concentration of the indicated component than the mole% concentration of the original stream it forms. "depleted" and "lean" do not mean that the flow is completely devoid of the indicated component.
The term "enriched" or "enriched" refers to having a greater mole% concentration of a specified component than the original stream it forms.
As used herein, "fluid communication" or "fluid flow communication" means operatively connected by one or more conduits, manifolds, valves, or the like, for conveying fluids. A conduit is any pipe, conduit, passage, etc. through which a fluid may be transported. Unless expressly stated otherwise, an intermediate device such as a pump, compressor, or vessel may be present between the first device in fluid flow communication with the second device.
Downstream and upstream refer to the intended direction of flow of the diverted process fluid. If the intended direction of flow of the process fluid is from a first device to a second device, the second device is downstream of the first device. In the case of a recycle stream, downstream and upstream refer to the first pass of the process fluid.
For purposes of simplicity and clarity, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.
The apparatus and method of the present invention are described with reference to the accompanying drawings. In the present disclosure, a single reference number may be used to identify the process gas stream and the process gas delivery line carrying the process gas stream. The features referred to by reference numerals will be understood from the context.
The apparatus and process of the present invention are used to separate a feed gas 11 containing light inert gas and at least one other gaseous component into a light inert gas-rich product gas 25 and a light inert gas-lean product gas 14. The light inert gas may be helium, neon or argon.
The feed gas 11 may be natural gas. The light inert gas may be helium. The at least one other component may be methane. Another component may be nitrogen. Some sources of natural gas are known to include methane, nitrogen and helium.
The feed gas 11 may be a non-condensable vent gas from an Air Separation Unit (ASU). The light inert gas may be neon. The at least one other component may be nitrogen. Another component may be oxygen. Another component may be argon. Air is known to contain nitrogen, oxygen, argon and neon.
The feed gas 11 may be natural gas. The light inert gas may be argon. The at least one other component may be methane. Another component may be carbon dioxide. Another component may be nitrogen. Some sources of natural gas are known to include methane, carbon dioxide, nitrogen and argon.
The apparatus comprises an adsorptive separation unit 10. An adsorptive separation unit is any separation unit that uses a solid adsorbent to separate a feed stream into at least two streams, one rich in more readily adsorbable species and the other rich in less adsorbable species. The adsorptive separation unit 10 includes a plurality of vessels 100a, 100b, 100c, 100d, 100 c. Each of the plurality of vessels contains an adsorbent bed adapted to separate the light inert gas from the other components in the feed stream.
The adsorptive separation unit typically comprises a plurality of adsorbent beds containing a suitable adsorbent. Fig. 1-3 provide an exemplary adsorption unit having five adsorption beds, and any suitable number of adsorption beds may be used. Typically, the number of adsorbent beds used in the adsorptive separation unit and process are designed to meet the desired product purity and recovery of the light inert gas product.
The number of beds can be a trade-off between capital and light inert gas recovery for the desired product purity. For example, increasing the number of beds allows the adsorption process to utilize a greater number of pressure equalization steps. The pressure equalization step is a light inert gas saving step. Increasing the number of pressure equalization steps will reduce the pressure at which gas is discharged from the bed to the waste stream, thereby reducing light inert gas losses. If the pressure equalization step is performed by cocurrent depressurization of the high-pressure bed, the impurity front proceeds further as more pressure equalization steps are used. In order to maintain the desired yield, the size of each bed is increased in addition to the number of beds. The degree of pressurization is reduced by reducing the number of pressure equalization steps, but may also be reduced by reducing the total number of moles of gas transferred in one or more pressure equalization steps, or by any combination of the two methods.
Alternatively, the number of beds may be increased to extend the time available for each step, which may limit the efficiency of the overall process. For example, increasing the number of beds allows the adsorption process to increase the number of beds that will process the feed gas or process the purge gas. Sending gas to more beds or more beds during purging reduces the velocity of the gas through the adsorbent particles, which improves the efficiency of the process step.
Typically, more than one adsorbent bed is used, such that at least one adsorbent bed can produce product gas while another bed is regenerated. In this way, a continuous production of product gas is possible.
FIG. 1 shows a 5-bed adsorptive separation unit having beds A-E. Fig. 2 shows an adsorption separation unit 10 having 5 adsorption vessels 100a, 100b, 100c, 100d, and 100 e. The skilled person can easily select the number of adsorption vessels/beds used.
The adsorbent bed may contain a single adsorbent or multiple adsorbents. In the case of multiple adsorbents, the adsorbents may be interspersed, layered, or a combination thereof.
One skilled in the art can readily select a suitable adsorbent. Suitable adsorbents for separating helium from other gaseous components in natural gas include activated carbon, silica gel, activated alumina, covalent organic frameworks, metal organic frameworks and zeolites.
The adsorptive separation unit may be operated using any known adsorption cycle suitable for separating light inert gas from a gas mixture comprising light inert gas and at least one other gaseous component. Examples are illustrated in US4077779A and US774068B2, both of which detail a pressure swing adsorption cycle for light gas purification.
The adsorption cycle may be a so-called Vacuum Pressure Swing Adsorption (VPSA) cycle.
The adsorption cycle may include a production step, a co-current flush step, a blowdown step, an evacuation step, and a product pressurization step. In the exemplary embodiment shown in fig. 1, the adsorbent bed AE is shown in a cycle with a production step (P), a co-current rinse step (R), a blowdown step (BD), an evacuation step (EV), and a product pressurization step (PP). During the adsorption cycle, each bed cycles through the cycle steps in turn. The corresponding VPSA cycle for the 5-bed adsorptive separation unit is shown in figure 3.
The production step is abbreviated herein as "P". The production step is also referred to in the literature as the feed step and/or the adsorption step.
As shown in FIG. 2, the adsorption separation unit 10 includes a feed gas header 200. A feed gas header 200 is in selective fluid communication with each of the plurality of vessels 100a, 100b, 100c, 100d, and 100e to provide a respective portion of the separation unit feed gas stream 12 to each of the plurality of vessels. By "selective" fluid communication is meant that a valve or equivalent means is used to selectively provide fluid communication between the components (i.e., between the feed gas header and each of the plurality of vessels). As shown in fig. 2, valve 110a provides selective fluid communication between feed gas header 200 and adsorption vessel 100a, valve 110b provides selective fluid communication between feed gas header 200 and adsorption vessel 100b, and so on.
In the embodiment shown in fig. 1 and 3, adsorber vessel feed gas 15 comprises combined gas stream 12 and rinse gas effluent 18 from the adsorber vessel undergoing the rinse step. In the embodiment illustrated in FIG. 2, feed gas header 200 receives combined gas stream 12 and rinse gas effluent 18 from an adsorption vessel undergoing a rinse step through rinse gas effluent header 250. Rinse gas effluent header 250 may or may not be used according to the adsorption cycle selected. The combined gas stream 12 is formed from the permeate stream 41 and the second gas stream 17 (discussed in more detail below).
Adsorber vessel feed gas 15 passes from feed gas header 200 through the corresponding open feed gas valve 110 (valve 110a for vessel 100a, valve 110b for vessel 100b, etc.) and into the corresponding adsorber vessel 100 for the production step of the adsorption cycle.
In the production step, an adsorption vessel feed gas stream 15 containing a light inert gas (e.g., helium) is introduced at feed gas pressure to the adsorbent bed undergoing the production step, and the secondary gas components (e.g., CH4 and N2) are adsorbed on the adsorbent in the adsorbent bed undergoing the production step, while a light inert gas-rich intermediate stream 13 is simultaneously withdrawn from the adsorbent bed undergoing the production step and passed to product gas header 210. A product gas header 210 is in selective fluid communication with each of the plurality of vessels 100a, 100b, 100c, 100d and 100e for receiving the light inert gas enriched intermediate gas 13 from each of the plurality of vessels during the production step. Product gas manifold 210 is in selective fluid communication with each respective vessel 100 through a respective product valve 113 (valve 113a for vessel 100a, valve 113b for vessel 100b, etc.). Light inert gas enriched intermediate gas 13 contains a higher concentration of light inert gas than adsorption vessel feed gas stream 15 and is depleted in secondary gas components. The duration of the production step may be any suitable duration, for example 1 to 300 seconds, or 30 to 300 seconds. The skilled person can readily determine the appropriate duration of any known adsorption cycle step.
The pressure in the adsorption bed subjected to the preparation step may be, for example, 0.1MPa to 3.4MPa or 0.3MPa to 1.2MPa (absolute pressure).
Each adsorbent bed has a "feed end" and a "product end" because they function in the production steps of the adsorption cycle. The feed gas mixture is introduced into the "feed end" of the adsorbent bed and product gas is withdrawn from the "product end" in a cyclic production step. In other steps of the adsorption cycle, gas may be introduced or withdrawn from the "feed end". Also, gas may be introduced or withdrawn from the "product side" during other steps of the adsorption cycle.
The flow direction during the other steps is generally described with reference to the flow direction during the production step. Thus, the gas flow in the same direction as the gas flow in the production step is "co-current" (sometimes referred to as "co-current"), and the gas flow in the opposite direction to the gas flow in the production step is "counter-current". The simultaneous introduction of gases into the adsorbent bed means that the gases are introduced in the same direction (i.e., into the feed end) as the feed gases introduced during the production step. The countercurrent introduction of gas into the adsorbent bed means that the gas is introduced in a direction opposite to the direction of the feed gas flow (i.e., into the product end) during the feed step. Simultaneous withdrawal of gas from the adsorbent bed means that gas is withdrawn in the same direction as the product gas (i.e. from the product end) during the production step. Countercurrent withdrawal of gas from the adsorbent bed means that gas is withdrawn in a direction opposite to the direction of product gas flow during the production step (i.e., withdrawal from the feed end).
The blowdown step (abbreviated "BD") comprises counter-currently withdrawing blowdown gas from the adsorbent bed undergoing the blowdown step. The blowdown gas has a concentration of the secondary gas component that is higher than the concentration of the secondary gas component in the adsorber vessel feed gas stream 15. Blowdown gas may be withdrawn from the adsorbent bed undergoing the counter-current blowdown step until the pressure in the adsorbent bed undergoing the counter-current blowdown step reaches a blowdown pressure of 40kPa to 1000 kPa. The blowdown pressure is the pressure in the adsorbent bed at the end of the counter current blowdown step.
As shown in fig. 1, blowdown gas may be passed from the adsorbent bed undergoing the blowdown step to a buffer vessel 70 and compressed in a compressor 56 to form rinse gas 19, "R" for the rinse step. As shown in fig. 2, the blowdown gas passes through blowdown gas header 230, surge tank 70, compressor 56, and into a flush gas supply header 240. The purge gas supply header 240 may or may not be used depending on the adsorption cycle selected.
The rinsing step is abbreviated as "R". The rinse step includes simultaneously introducing rinse gas 19 into the adsorbent bed undergoing the rinse step while simultaneously withdrawing rinse gas effluent 18 from the adsorbent bed undergoing the rinse step. The displacement of the more strongly adsorbed component from the adsorbent and void spaces during the rinse step provides a means to increase the recovery of the less strongly adsorbed component, i.e., the light inert gas. A rinse gas may be formed from the blowdown gas. The rinse gas may also be formed from a light inert gas depleted intermediate stream, an external gas source free of light inert gas, or any combination thereof.
As shown in fig. 1, rinse gas effluent stream 18 can be introduced into the adsorption bed undergoing production step "P" along with adsorption separation unit feed gas stream 12 as adsorption vessel feed gas stream 15.
The formation of the rinse gas from the blowdown gas, in combination with the rinse step, in combination with the introduction of the rinse gas effluent into the adsorbent bed undergoing the production step, has the technical effect of increasing the recovery of light inert gas.
As shown in fig. 1, the adsorption cycle may also include an evacuation step "EV". The evacuation step is similar to the blowdown step, with the addition of a compressor, vacuum pump, or the like 57 to reduce the pressure to below atmospheric. The gas evacuated from the adsorption bed undergoing the evacuation step is sent to an off-gas header 220 and then to the compressor 57 where it is discharged from the compressor 57 as a tail gas stream 51.
An off-gas header 220 is in selective fluid communication with each vessel of the plurality of vessels for receiving the light inert gas-lean gas from each vessel of the plurality of vessels. Selective fluid communication between the off-gas header and each respective adsorption vessel 100 is provided by valves 115 and 116 (115 a and 116a for vessel 100a, 115b and 116b for vessel 100b, etc.). The off-gas header 220 is in fluid communication with the outlet of the adsorption separation unit 10 for discharging the light inert-lean gas from the adsorption separation unit 10. For the case where feed gas stream 11 is natural gas containing helium, tail gas stream 51 is natural gas depleted of helium and may be introduced into a natural gas pipeline for any desired use.
Depending on the adsorption cycle used, the blowdown gas header may also be an off-gas header, for example when the blowdown gas is discharged from the adsorption separation unit 10 as a light inert-lean gas.
As shown in fig. 1, the adsorption cycle may also include a product pressurization step "PP". The product pressurization step includes counter-currently introducing a portion of the product gas 16 into the bed to pressurize the vessel. As shown in FIG. 2, product gas 16 may be introduced into a respective adsorption vessel 100 from a product gas header 210 through a respective product gas valve 113. Product gas 16 can be introduced into the adsorbent bed undergoing the product pressurization step until the adsorbent bed undergoing the product pressurization step is substantially at the feed gas pressure.
The adsorption cycle may include various other adsorption cycle steps, such as a pressure equalization step, if desired. Various adsorption cycle steps are discussed, for example, in U.S. patent No.9,381,460.
The adsorption cycle has a cycle time. Cycle time is a term well known in the art. The adsorption separation unit undergoes a series of repeated cycling steps that define an adsorption cycle. Cycle time is the time required to complete one adsorption cycle from start to finish.
A plurality of vessels 100a, 100b, 100c, 100d, 100e are operatively connected to various manifolds 200, 210, 220, 230, 240 and 250 by respective process gas delivery lines 101, 102, 103, 104, 105, 106107 and 108. As used herein, a process gas delivery line is any fluid tight transfer device, such as a pipe, conduit, hose, or the like, for transferring a process gas therein.
Each of the plurality of vessels 100a, 100b, 100c, 100d, 100e has a process gas transfer line associated therewith (process gas transfer lines 101a, 102a, 103a, 104a, 105a, 106a, 107a, and 108a for vessel 100 a; process gas transfer lines 101b, 102b, 103b, 104b, 105b, 106b, 107b, and 108b for vessel 100 b; process gas transfer lines 101c, 102c, 103c, 104c, 105c, 106c, 107c, and 108c for vessel 100 c; process gas transfer lines 101d, 102d, 103d, 104d, 105d, 106d, 107d, and 108d for vessel 100 d; and process gas transfer lines 101e, 102e, 103e, 104e, and 108e for vessel 100 e). Process gas delivery lines are "associated" with a particular vessel if they provide fluid communication between the particular vessel and an adjacent header. The process gas delivery lines are associated with a particular vessel if they are operably disposed between the particular vessel and an adjacent header (and not outside the adjacent header). Referring to fig. 2, only the "a" process gas delivery line is associated with vessel 100a, only the "b" process gas delivery line is associated with vessel 100b, only the "c" process gas delivery line is associated with vessel 100c, only the "d" process gas delivery line is associated with vessel 100d, and only the "e" process gas delivery line is associated with vessel 100 e.
As shown in FIG. 2, there are a plurality of valves in the process gas delivery line ( valves 110a, 111a, 112a, 113a, 114a, 115a and 116a for vessel 100 a; valves 110b, 111b, 112b, 113b, 114b, 115b and 116b for vessel 100 b; valves 110c, 111c, 112c, 113c, 114c, 115c and 116c for vessel 100 c; valves 110d, 111d, 112d, 113d, 114d, 115d and 116d for vessel 100 d; valves 110e, 111e, 112e, 113e, 114e, 115e and 116e for vessel 100e) that include a plurality of valves adjacent to and associated with each respective vessel 100. Valves control the flow of process gas into and out of the adsorption vessels 100a, 100b, 100c, 100d, and 100e to achieve various cycle steps.
A valve is "associated" with a particular container if the valve is operably disposed between the particular container and an adjacent header (and not outside of the adjacent header). A valve associated with a particular vessel may control flow between the particular vessel and an adjacent manifold.
A valve is "adjacent" to a vessel if no other valve is operably disposed in the process gas delivery line between the valve and the vessel; no valves are inserted in the process gas delivery lines between adjacent valves and the respective containers. A valve in the process gas delivery line is operably disposed between the second valve and the container and when closed will prevent the flow of process gas from the second valve to the container or from the container to the second valve.
Referring to fig. 2, valves 110a, 111a, 112a, 113a, 114a, and 115a are associated with and adjacent to container 100 a. The valve 116a is associated with the container 100a but is not adjacent to the container 100a because the valve 115a is operably disposed between the container 100a and the valve 116 a. Likewise, valves 110b, 111b, 112b, 113b, 114b, and 115b are associated with and adjacent to container 100 b. The valve 116b is associated with the container 100b but is not adjacent to the container 100b because the valve 115b is operably disposed between the container 100b and the valve 116 b.
The apparatus of the invention is characterized by an adsorption separation unit 10 configured to maintain a process gas delivery line volume and dead end volume, which is filled with a quantity of light inert gas during a pressurization step and evacuated through an off-gas header during a depressurization step below a threshold level. These specific volumes are such as to carry a significant amount of light inert gas out of the system in the stream not captured in the light inert gas product stream. That is, these volumes reduce the light inert gas recovery efficiency.
The separation unit structure may be defined according to the central volume and the second volume of each of the containers 100a, 100b, 100c, 100d, and 100e, as described below.
The central volume of each vessel 100 is a designated volume of the process gas delivery line associated with each respective vessel 100. The central volume of each respective container is the sum of:
(i) the volume contained in the process gas delivery line associated with the respective container, each valve 110, 111, 112, 113, 114, 115 connecting said respective container to the vicinity of the respective container 100,
(ii) all dead-end volumes 109, if any, are connected to respective containers 100 at junctions, and
(iii) all dead-end volumes (not shown), if any, are connected at junctions to any process gas delivery lines associated with the respective vessels 100, connecting the respective vessels 100 to any valves 110, 111, 112, 113, 114, 115 adjacent the respective vessels 100.
The central volume of the container 100 does not include the volume of the container itself.
A detailed description of the process gas delivery lines that make up the central volume of the vessel 100a will be provided. The process gas delivery lines that make up the central volumes of the vessels 100b, 100c, 100d, and 100e should be understood from this detailed description, and the reference numerals have been changed as necessary (i.e., "b" instead of "a" for vessel 100b, "c" instead of "a" for vessel 100c, "" d "instead of" a "for vessel 100d," and "e" instead of "a" for vessel 100 e).
The central volume of the vessel 100a includes (i) the volume contained in the process gas delivery line associated with the vessel 100a, connecting the vessel 100a to each valve in the vicinity of the vessel 100 a. Referring to fig. 2, the valves near the container 100a include valves 110a, 111a, 112a, 113a, 114a, and 115 a. The process gas delivery lines associated with vessel 100a and connecting vessel 100a to the valves include process gas delivery lines 102a, 103a, 104a, 105a, 107a, and 108 a. A process gas delivery line 102a connects the vessel 100a to a nearby valve 110 a. A process gas delivery line 103a connects the vessel 100a to a nearby valve 111 a. A process gas delivery line 104a connects the vessel 100a to a nearby valve 112 a. A process gas delivery line 105a connects the vessel 100a to a nearby valve 113 a. A process gas delivery line 107a connects the vessel 100a to a nearby valve 114 a. A process gas delivery line 108a connects the vessel 100a to a nearby valve 115 a.
The central volume of the vessel 100a includes (ii) all dead-end volumes, if any, connected to the respective vessel 100 at a junction.
A "dead-end volume" is defined as a volume in continuous open fluid communication with a respective vessel that allows for the ingress and egress of process gas only at the junction of the dead-end volumes. By "continuous open fluid communication" is meant that the dead-end volume is in continuous fluid communication with the respective container during the process. No valves or other devices shut off the fluid communication of the dead-end volumes with the respective containers.
Referring to fig. 2, the process gas sensor line 109a is such a dead-end volume.
The adsorptive separation unit 10 may be configured with no dead-end volume connected at the connection to any vessel 100.
The central volume of the container 100a includes: (iii) all dead end volumes, if any, are connected at junctions to any process gas delivery lines associated with vessel 100a, connecting vessel 100a to any valves 110a, 111a, 112a, 113a, 114a, 115a adjacent vessel 100 a. The process gas delivery lines associated with vessel 100a and connecting vessel 100a to nearby valves 110a, 111a, 112a, 113a, 114a, 115a include process gas delivery lines 102a, 103a, 104a, 105a, 107a, and 108 a. Figure 2 shows no such dead end volume. However, if the sensor line 109a is moved into engagement with the process gas delivery line 105a rather than the vessel 100a, there will be one such dead-end volume.
The central volume of each container having a corresponding volume Vc。
The central volume of each respective container includes a second volume that is a subset of the central volume. The second volume is an undesirable volume that reduces the efficiency of light inert gas recovery.
The second volume of each respective container 100 is the sum of:
(i) all volumes of dead-end volume, if any, are connected to the respective container 100,
(ii) the volume of all dead-end volumes, if any, connected at junctions to any process gas delivery lines associated with the respective vessel 100, connects the respective vessel 100 to any valve 110, 111, 112, 113, 114, 115 adjacent the respective vessel 100; and
(iii) the volume of any process gas delivery line, if any, has a first end terminating in a valve adjacent the respective vessel 100 configured to allow process gas to be transferred to the off-gas header 220 when opened, and has a second end terminating at a junction in any other associated process gas delivery line connecting the respective vessel 100 to any other valve 110 adjacent the respective vessel 100.
The second volume of the container 100 does not include the volume of the container itself.
A detailed description of the process gas delivery lines that make up the second volume of the vessel 100a will be provided. The process gas delivery lines that make up the second volumes of the vessels 100b, 100c, 100d, and 100e should be understood from this detailed description, and the reference numerals have been changed as necessary (i.e., "b" instead of "a" for vessel 100b, "c" instead of "a" for vessel 100c, "" d "instead of" a "for vessel 100d," and "e" instead of "a" for vessel 100 e).
The second volume of the container 100a includes (i) all dead end volumes, if any, connected to the respective container 100 at a junction.
Referring to fig. 2, process gas sensor line 109a is such dead-end volume according to standard (i).
The adsorptive separation unit 10 may be configured with no dead-end volume connected at the connection to any vessel 100.
The second volume of the container 100a includes: (ii) all dead end volumes, if any, are connected at junctions to any process gas delivery lines associated with vessel 100a, connecting vessel 100a to any valves 110a, 111a, 112a, 113a, 114a, 115a adjacent vessel 100 a. The process gas delivery lines associated with vessel 100a and connecting vessel 100a to nearby valves 110a, 111a, 112a, 113a, 114a, 115a include process gas delivery lines 102a, 103a, 104a, 105a, 107a, and 108 a. Figure 2 shows no such dead end volume. However, if the sensor line 109a is moved into engagement with the process gas delivery line 105a rather than the vessel 100a, there will be one such dead-end volume.
The second volume of the container 100a includes: (iii) the volume of any process gas delivery line, if any, has a first end terminating in a valve adjacent the respective vessel 100a configured to allow the process gas to be transferred to the off-gas header 220 when opened, and has a second end terminating at a junction with any other associated process gas delivery line, connecting the respective vessel 100a to any other valve adjacent the respective vessel 100 a. Referring to fig. 2, the process gas delivery line 108a has a first end terminating in a valve 115a, the valve 115a being adjacent the vessel 100 a. The valve 115a is configured to allow the process gas to be delivered to the exhaust header 220 when open. A second end of the process gas delivery line 108a terminates at a connection to the process gas delivery line 102a, the process gas delivery line 102a connecting the vessel 100a to a valve 110a adjacent the vessel 100 a. Thus, the process gas delivery line 108a is the volume that contributes to the second volume according to criterion (iii).
Each container having a corresponding second volume V2。
We have found that the second volume of the adsorptive separation unit has an effect on the recovery efficiency of the light inert gas, with the feed gas components having a low concentration of light inert gas.
By providing an adsorptive separation unit having a second volume that is much smaller than the central volume, more light inert gas can be supplied to the purification unit to meet the final product purity specifications of the system.
Accordingly, it is desirable to construct the adsorptive separation unit 10 with a second volume that is smaller relative to the central volume. For each container 100, the second volume V2May be smaller than the central volume V c5%, or less than 3%, or less than 1%. Second volume V2May be 0.
An isolation valve (not shown) may be used to reduce the second volume. For example, referring to vessel 100a in fig. 2, an isolation valve (not shown) may be positioned in process gas delivery line 102a between vessel 100a and valve 115 a. In this case, the valve 115a is no longer an adjacent valve. The isolation valve may be operated to prevent the process gas delivery line 108a from being filled with product gas having a higher concentration of light inert gas during repressurization. The process gas delivery line 108a can be repressurized with a purge gas having a lower concentration of light inert gas during the purge step. However, the use of isolation valves during an adsorption cycle adds complexity with respect to the time to open and close the isolation valves.
Also not shown are process gas delivery lines and valves associated with each vessel for by-pass, venting, start-up, shut-down, maintenance, etc., which are well known and commonly used in adsorptive separation units. These process gas delivery lines may also contribute to the central volume and the second volume.
The apparatus of the present invention may also include a purification unit 20. The purification unit may be an adsorption type separation unit, a rapid cycle adsorption unit, a membrane type separation unit, or a distillation type separation unit.
An adsorptive separation unit is any separation unit that uses adsorption to separate a feed stream into at least two streams, each stream having a different concentration of a substance. As used herein, the term "adsorption" includes any separation in which components are separated by the relative adhesion of a substance (atom, ion or molecule) to the surface of an adsorbent.
The adsorption cycle has a cycle time. Cycle time is a term well known in the art. The adsorption separation unit undergoes a series of repeated cycling steps that define an adsorption cycle. Cycle time is the time required to complete one adsorption cycle from start to finish.
A rapid cycle adsorption unit is any adsorptive separation unit that uses rapid cycles. Rapid cycling is discussed in more detail in U.S. patent applications 16/102,936 and 16/103,569, both filed 8/14/2018, both incorporated herein by reference. As used herein, the term "rapid" refers to the total duration of a cyclical production step, also referred to as a feed step and/or an adsorption step, preferably 45 seconds or less, the production step being a cyclical step in which the adsorbent bed is at an elevated pressure (relative to the pressure in the bed in other steps of the process), and the feed stream is introduced into and passed through the bed to adsorb one or more components from the feed stream to produce a product stream exiting the bed that is depleted in the adsorbed component (relative to the composition of the feed stream), as is well known in the art. The total duration of the production step of the cycle may be at least 3 seconds. The total duration of the production step may be 3 to 45 seconds, or 3 to 16 seconds.
A rapid cycle adsorption unit may have a cycle time of 100 seconds or less, which is the amount of time it takes to complete a full set of steps of an adsorption cycle. Further, the rapid cycle adsorption unit may have a cycle time of 60 seconds or less, 50 seconds or less, or 40 seconds or less. The rapid cycle adsorption unit may have a cycle time of at least 15 seconds.
The adsorbent bed may be packed with conventional randomly packed adsorbents or structured adsorbents (in monoliths, laminates or perforated forms). It has been determined that structured adsorbents help reduce the deleterious effects of mass transfer resistance and flow friction pressure drop of fast cycle adsorption units operating at higher cycle frequencies.
The membrane separation unit may be any separation unit that uses a membrane to separate a feed stream into two streams, which is defined in the same manner as when the feed membrane separation unit was previously discussed, wherein the membrane may be a single membrane unit or a plurality of membranes in series or in parallel.
A distillative separation unit is any separation unit that uses distillation to separate a feed stream into two streams, each stream having a different concentration of a substance. As used herein, the term "distillation" includes any separation of components by their relative volatility. Other terms used in the industry include fractionation, rectification and partial condensation.
The purification unit 20 has an inlet, a first outlet and a second outlet. The inlet is in fluid communication with the product gas header 210 of the adsorptive separation unit 10. An inlet of the purification unit 20 is operably configured to receive at least a portion of the light inert gas-enriched intermediate gas 13 from the product gas header 210. Light inert gas depleted intermediate gas 23 is discharged from the first outlet of the purification unit 20. A light inert gas-enriched product gas 25 exits from a second outlet of the purification unit 20.
The apparatus of the present invention may include a gas mixer 60. The gas mixer 60 has a first inlet for receiving the feed gas 11, a second inlet in fluid communication with a second gas source 17, and an outlet. The gas mixer 60 may be a mixing tee, a mixing vessel, a static mixer, or any other suitable mixing device capable of combining multiple streams to form a mixed stream comprising multiple streams. The second inlet of the gas mixer 60 receives a second gas 17 from a second gas source, wherein the second gas has a higher light inert gas content than the feed gas 11. The second gas source may be a first outlet of the purification unit 20. The second gas 17 may comprise a light inert gas depleted intermediate gas 23 from the purification unit 20. The apparatus may include a compressor 45 for compressing the light inert gas depleted intermediate gas 23 before the light inert gas depleted intermediate gas 23 is fed into the gas mixer 60. Separation unit feed gas 12 is formed from feed gas 11 and light inert gas depleted intermediate gas 23 and exits the outlet of gas mixer 60 and is passed to feed gas header 200 of adsorption separation unit 10.
The feed gas header 200 of the adsorption separation unit 10 is in downstream fluid communication with the outlet of the gas mixer 60. The feed gas header 200 of the adsorption separation unit 10 is operably configured to receive the separation unit feed gas 12 from the gas mixer 60.
The apparatus may include a sensor 50, the sensor 50 being operatively arranged to detect a measure of helium content and to transmit a signal in response thereto. The sensor 50 may be located in the process gas delivery line 11 that supplies the first inlet of the gas mixer 60. In this position, the sensor 50 is operatively arranged to detect a measure of the light inert gas content in the feed gas 11. As shown in fig. 1, the sensor may be located in the process gas delivery line 12 connecting the outlet of the gas mixer 60 to the feed gas header 200 of the adsorption separation unit 10. At this location, sensor 50 is operably configured to detect a measure of the light inert gas content of the separation unit feed gas 12. Alternatively, sensor 50 may be located in feed gas header 200. In this position, sensor 50 is operatively arranged to detect a measure of the light inert gas content of the adsorber vessel feed gas 15.
More than one sensor 50 may be used. Where more than one sensor 50 is used, one or more sensors may be present in the process gas delivery line 11 supplying the first inlet of the gas mixer 60 and/or in the process gas delivery line 12 connecting the outlet of the gas mixer 60 to the feed gas header 200 of the adsorptive separation unit 10 and/or in the feed gas header 200.
A measure of the light inert gas content may be the light inert gas concentration. The measured light inert gas concentration may be determined by a concentration sensor 50 that detects the light inert gas concentration. The measured light inert gas concentration may be a mole fraction, a mass fraction, a mole%, a mass%, a volume%, or any other suitable concentration unit. The light inert gas concentration may be any light inert gas concentration unit.
The apparatus may include a controller 80 in signal communication with the sensor 50. The signal communication may be wireless or hardwired. The controller is operable to control the operating conditions of the purification unit 20 in response to signals from the sensor 50. In response to the measurement of the light inert gas content, the purification unit 20 is controlled to adjust the flow rate of the light inert gas in the second gas stream 17.
The second inlet of the gas mixer 60 may be in fluid communication with a second outlet of the purification unit 20. The gas mixer 60 can receive a portion 28 of the light inert gas-enriched product gas 25 from the purification unit 20.
The purification unit 20 may include a flow regulator 29 operably disposed between the second inlet of the gas mixer 60 and the second outlet of the purification unit 20. The controller 80 is operable to control the purification unit 20 by adjusting the flow regulator 29. The flow regulator regulates the flow rate of the portion 28 of the light inert gas-enriched product gas 25 from the purification unit 20 to the gas mixer 60 to vary the content of the light inert gas entering the adsorptive separation unit 10. Controller 80 adjusts flow regulator 29 in response to the measurement of the light inert gas content determined by sensor 50.
The apparatus may include a flow regulator 33 operatively disposed between the second inlet of the gas mixer 60 and the process gas delivery line 36. The flow regulator 33 may be in signal communication with a controller 80. The signal communication may be wireless or wired. The controller 80 may be used to control the flow rate of the light inert gas from the process gas delivery line 36 by adjusting a flow regulator 33 operatively disposed between the second inlet of the gas mixer 60 and the process gas delivery line 36. The flow regulator 33 may regulate the flow rate of a portion of the light inert gas-enriched intermediate stream from the adsorption separation unit 10 to the second inlet of the gas mixer 60 to vary the content of the light inert gas supplied to the adsorption separation unit 10. The controller 80 may adjust the flow regulator 33 in response to the measurement of the light inert gas content determined by the sensor 50.
In another embodiment, the gas mixer 60 may have a third inlet. The third inlet may be in fluid communication with a second outlet of the purification unit 20. A third inlet of the gas mixer 60 can receive a portion 28 of the light inert gas-enriched product gas 25 from the purification unit 20.
The purification unit 20 can include a flow regulator 31 in signal communication with the controller 80 and operably disposed between the third inlet of the gas mixer 60 and the second outlet of the purification unit 20. The controller 80 is operable to control the purification unit 20 by adjusting the flow regulator 31. Flow regulator 31 regulates the flow rate of portion 28 of light inert gas-enriched product gas 25 from purification unit 20 to the third inlet of gas mixer 60 to vary the content of light inert gas flowing to adsorptive separation unit 10. The controller 80 adjusts the flow regulator 31 in response to the measurement of the light inert gas content determined by the sensor 50.
Alternatively or additionally, the third inlet of the gas mixer 60 may be in fluid communication with a process gas transfer line 36, the process gas transfer line 36 operatively connecting the product gas header 210 of the adsorptive separation unit 10 to the inlet of the purification unit 20.
The apparatus may include a flow regulator 37 operatively disposed between the third inlet of the gas mixer 60 and the process gas delivery line 36. The flow regulator 37 may be in signal communication with a controller 80. The signal communication may be wireless or wired. The controller 80 may be used to control the flow rate of the light inert gas from the process gas delivery line 36 by adjusting a flow regulator 37 operatively disposed between the third inlet of the gas mixer 60 and the process gas delivery line 36. The flow regulator 37 may regulate the flow rate of a portion of the light inert gas-enriched intermediate stream from the adsorption separation unit 10 to the third inlet of the gas mixer 60 to vary the content of the light inert gas supplied to the adsorption separation unit 10. The controller 80 may adjust the flow regulator 37 in response to the measurement of the light inert gas content determined by the sensor 50.
The purification unit 20 may be a membrane separation unit. The membrane separation unit may be any membrane device that has a certain selectivity for separating the light inert gas from the other components in the feed while maintaining a pressure differential across the membrane. When the light inert gas is helium, the helium permeability through the membrane is typically greater than the helium permeability of the other components present in the membrane feed. Thus, the helium concentration in the non-permeate stream from the membrane separation unit is less than the concentration in the feed stream to the membrane separation unit. Typically, the pressure of the helium depleted non-permeate stream is 10 to 200kPa lower than the feed stream to the membrane separation unit. The light inert gas-enriched product permeate stream can have a pressure of from 100kPa to 500kPa or from 100kPa to 350 kPa. Higher helium permeability and/or its selectivity across the membrane are required and have a beneficial effect on the performance of the overall system.
When the purification unit 20 is a membrane-based separation unit, the membrane unit may consist of a single membrane device, or alternatively, a plurality of membrane devices, configured and operated to achieve separation in the most efficient manner, e.g., cascaded membranes with internal recycle streams between various stages of the membrane unit. Typically, membrane devices are manufactured in modules, each module having certain semi-permeable membrane regions for permeation.
Sanders et al (Polymer; vo 154; pp 4729-4761; 2013), which are incorporated herein by reference, provide a convenient overview of current film technology. They describe the physical parameters and performance characteristics of polymer membranes, including polysulfones, cellulose acetates, aramids, polyimides, and polycarbonates. Essentially all currently industrially useful gas separations are carried out using polymeric (such as those listed above) or rubber materials (such as siloxanes). Other membrane materials such as mixed matrix membranes, perfluoropolymers, thermally rearranged polymers, facilitated transport membranes, metal-organic frameworks, zeolite-imidazolate frameworks and carbon molecular sieves are in different stages of development. The membrane material in the membrane separation unit of the present invention may be any of those listed above, or any other material having a faster permeation rate for certain compounds, such as helium, and a slower permeation rate for certain compounds, such as methane.
Membrane separation units having some selectivity for separating light inert gases such as helium and neon are commercially available, for example, from air products, L' air Liquide, Ube, Cameron and UOP.
As shown in fig. 1, the apparatus may include a buffer tank 30, and the light inert gas enriched intermediate stream 13 may be passed from the adsorptive separation unit 10 to the buffer tank 30 before being passed to the second membrane separation unit 20. The tank buffers pressure fluctuations and light inert gas concentrations of the light inert gas enriched intermediate stream 13 from the adsorptive separation unit 10. The uniform light inert gas concentration and pressure improves the controllability of the purification unit 20, particularly when the purification unit is a membrane-type device.
The membrane separation unit may include one or more adjustable orifices 26 operable to control the pressure in the membrane separation unit. The one or more adjustable orifices are operable to control the pressure differential between the second (membrane) separation unit feed gas stream 21 and the light inert gas-enriched product (permeate) stream 25.
The one or more adjustable orifices may be valves or functionally equivalent means for controlling flow and/or pressure. Fig. 1 shows a valve 26 in fluid communication with the second outlet of the second (membrane) separation unit 20 and a valve 27 in fluid communication with the first outlet of the second (membrane) separation unit 20. Valves 26 and 27 can be adjusted to control the pressure differential between purge unit feed gas stream 21 and light inert gas-enriched product (permeate) stream 25.
The pressure differential between the second (membrane) separation unit feed gas stream 21 and the light inert gas-enriched product (permeate) stream 25 can be increased or decreased by varying the percentage of the opening of the adjustable orifice (i.e., valve 27) in fluid communication with the first outlet for discharging the light inert gas depleted intermediate (non-permeate) stream 23 and varying the percentage of the opening of the adjustable orifice (i.e., valve 26) in fluid communication with the second outlet for discharging the light inert gas-enriched product (permeate) stream 25.
The one or more adjustable orifices may be valves or similar devices capable of controlling the pressure in the membrane separation unit. The one or more adjustable orifices may be in signal communication with the controller 80. The controller is operable to control the purification unit 20 by adjusting the one or more adjustable orifices 26. Increasing the back pressure on the permeate side of the membrane separation unit increases the flow rate of the light inert gas in the light inert gas depleted intermediate (non-permeate) stream. Reducing the back pressure on the permeate side of the membrane separation unit reduces the flow rate of the light inert gas in the light inert gas depleted intermediate (non-permeate) stream.
The membrane separation unit may comprise a plurality of membrane modules and one or more control valves which control the proportion of the membrane modules in operation. The one or more control valves may be in signal communication with the controller 80. The controller may be used to control the purification unit 20 by adjusting the fraction of membrane modules in operation. Increasing the proportion of membrane modules in operation reduces the flow rate of light inert gas in the light inert gas depleted intermediate (non-permeate) stream. Reducing the fraction of membrane modules in operation increases the flow rate of light inert gas in the light inert gas depleted intermediate (non-permeate) stream.
The membrane separation unit may include a heat exchanger 40. The heat exchanger 40 is operable to control the temperature in the purification unit 20. The heat exchanger is operably configured to selectively heat or cool at least a portion of purification unit feed gas stream 21 by indirect heat transfer with a heat transfer medium. The heat transfer medium may be a heat transfer fluid.
The heat exchanger 40 may be in signal communication with a controller 80. The signal communication may be wireless or hardwired. The controller 80 may be used to control the membrane separation unit by adjusting the heat load of the heat exchanger 40. Increasing the temperature of the stream entering the membrane separation unit reduces the flow rate of light inert gas in the light inert gas depleted intermediate (non-permeate) stream. Reducing the temperature of the stream entering the membrane separation unit increases the flow rate of light inert gas in the light inert gas depleted intermediate (non-permeate) stream.
As shown in FIG. 1, purification unit 20 can include a compressor 35 to compress purification unit feed gas stream 21.
The purification unit 20 may be an adsorption type separation unit.
The adsorptive separation unit may comprise a plurality of vessels, wherein each vessel contains a bed of adsorbent. The adsorptive separation unit may include one or more control valves that control portions of the plurality of vessels in transit. An adsorbent bed is "on-line" if it is undergoing an adsorption cycle to form a light inert gas depleted intermediate stream and a light inert gas-enriched product stream. An adsorbent bed is "off-line" if it is idle while other adsorbent beds in the system are undergoing an adsorption cycle. The one or more control valves may be in signal communication with the controller 80. The signal communication may be wireless or hardwired.
The second gas source may be a first outlet of the purification unit. The controller 80 may be used to control the flow rate of the light inert gas from the first outlet of the purification unit to the second inlet of the gas mixer 60 by adjusting the fraction of the plurality of vessels in operation. Increasing the ratio of multiple vessels in the flow decreases the flow rate of the light inert gas in the light inert gas depleted intermediate stream. Reducing the fraction of multiple vessels in operation increases the flow rate of the light inert gas in the light inert gas depleted intermediate stream.
The second gas source may be a first outlet of the purge unit, wherein the purge unit 20 comprises a feed gas header and one or more adjustable orifices 32 operative to control the pressure in the feed gas header. The controller 80 is operable to control the flow rate of the light inert gas from the second gas source 17 to the second inlet of the gas mixer 60 by adjusting one or more adjustable orifices 32 operable to control the pressure in the feed gas header of the purification unit 20. The one or more adjustable orifices 32 may be valves. Increasing the pressure in the feed gas header reduces the flow rate of the light inert gas in the light inert gas depleted intermediate stream. Reducing the pressure in the feed gas header increases the flow rate of the light inert gas in the light inert gas depleted intermediate stream.
The second gas source can be a first outlet of the purification unit, wherein the purification unit 20 comprises an exhaust gas header and one or more adjustable orifices 27 operable to control the pressure in the exhaust gas header. The controller 80 can be used to control the flow rate of the light inert gas from the second gas source 17 to the second inlet of the gas mixer 60 by adjusting one or more adjustable orifices 27 to control the pressure in the exhaust header. The one or more adjustable orifices 27 may be valves. Increasing the pressure in the off-gas header increases the flow rate of the light inert gas in the light inert gas depleted intermediate stream. Reducing the pressure in the off-gas header reduces the flow rate of the light inert gas in the light inert gas depleted intermediate stream.
The second gas source may comprise a second outlet of the purge unit, wherein the purge unit 20 comprises a product gas header and one or more adjustable orifices 29 operative to control the pressure in the product gas header. Controller 80 is operable to control the flow rate of light inert gas from second gas source 17 to the second inlet of gas mixer 60 by adjusting one or more adjustable orifices 29 to control the pressure in the product gas manifold. Increasing the pressure in the product gas header reduces the flow rate of the light inert gas in the light inert gas depleted intermediate stream. Reducing the pressure in the product gas header increases the flow rate of the light inert gas in the light inert gas depleted intermediate stream.
It is known in the art that temperature affects the adsorption process. For example, adsorption is exothermic and lower temperatures increase capacity. In contrast, desorption is endothermic and therefore regenerates the bed less effectively at lower temperatures. These competing forces result in an optimum temperature for a given working capacity of the bed. Operating at a temperature in the adsorptive separation unit near the optimum temperature for the working capacity will result in a lower flow rate of light inert gas in the light inert gas depleted intermediate stream than operating at a feed temperature away from the optimum temperature.
The purification unit 20 may be a rapid cycle adsorption unit. Any suitable apparatus for performing rapid cycle adsorption may be used. The conventional on-off valve is limited in opening and closing time and thus is not suitable for a rapid cycle adsorption method. The adsorption process using conventional on-off valves has associated piping with large volumes that shorten with cycling, reducing process efficiency. The rotary valve is continuously movable and has a small associated conduit volume when properly designed, overcoming both limitations of conventional on-off valves. Rotary valve rapid cycle adsorption processes can be carried out using rotary valve adsorption equipment in which the adsorption beds are located in fixed bed assemblies and switched between adsorption steps by rotating feed and product valves as is known in the art. The rotary feed valve effectively replaces all valves corresponding to each bed on the feed side and the rotary product valve effectively replaces all valves corresponding to each bed on the product side.
The fast cycle adsorption process may be carried out using a rotating bed fast cycle adsorption unit. For a rotating bed rapid cycle adsorption apparatus, the adsorbent beds are placed in a rotor assembly located between first and second stator assemblies, each adsorbent bed having a rotor port at either end of the bed through which gas can exit or enter the bed. The adsorption process involves a counter-current blowdown and purge step, typically a second stator assembly comprising at least one feed port, at least one drain port and a first stator plate having: at least one feed slot for directing at least one feed gas stream from the feed inlet into any one of the rotor ports aligned with the slot; at least one discharge slot for directing a flow of a discharge gas stream from any of the rotor ports aligned with the slot to the discharge port, and a second stator assembly including at least one product port and a second stator plate having: at least one product tank for directing at least one product gas stream to flow between the product port and any one of the rotor ports aligned with the tank; and at least one purge slot for directing a flow of at least one purge gas stream into any of the rotor ports aligned with the slot. The rotor assembly is rotated relative to the first and second stator assemblies to change the operating mode of each adsorption bed by changing which rotor ports are aligned with which slots in the first and second stator plates, wherein the bed is in a repressurization mode or a feed mode when the rotor ports of the bed are aligned with the feed slots and/or the product slots, the bed is in a purge mode when the rotor ports of the bed are aligned with the discharge slots and the purge slots, and it is in a blowdown mode when the rotor ports of the bed are aligned with the discharge slots and not aligned with the purge slots.
One skilled in the art will generally select between rotary bed and rotary valve rapid cycle adsorption units based on economies of scale and the number of beds required for a given separation. Smaller flow rates and more beds facilitate a rotating bed configuration and larger flow rates and fewer beds facilitate a rotary valve with a fixed bed.
The number of beds in a rapid cycle adsorption unit reflects a tradeoff between capital expenditure and process efficiency. For example, more beds may provide higher recovery of light inert gas, but process economics will dictate the upper limit on the number of beds. The overall recovery of the adsorption process is also higher for higher light inert gas concentrations in the feed. For the present application, where high recovery is not required and a relatively high concentration of light inert gas is present in the purification unit feed gas stream 21, the optimum number of beds is typically between 6 and 9, inclusive.
The adsorption cycle also includes a repressurization step, wherein the bed undergoing the repressurization step (i.e., the bed in the repressurization mode) is typically repressurized back to the pressure used for the feed step using the feed gas and/or the product gas. Repressurization with product gas will isolate the adsorption sites from impurities regardless of the overall system productivity. Repressurization with the feed gas will adsorb some of the adsorption sites with impurities, reducing the productivity of the bed. Increasing the ratio of feed flow to product flow during the repressurization step results in an increase in the flow rate of the light inert gas in the light inert gas depleted intermediate stream by reducing the available adsorption sites in the bed, which in turn reduces the recovery of light gases.
The purification unit 20 may be a distillation type separation unit.
The second gas source may be a first outlet of the purification unit 20, wherein the purification unit includes one or more adjustable orifices 26, 27, 32 in signal communication with a controller 80, the controller 80 operable to control the pressure in the purification unit 20. The controller 80 is operable to control the flow rate of the light inert gas from the second gas source 17 to the second inlet of the gas mixer 60 by adjusting the one or more adjustable orifices 26, 27, 32 to control the pressure in the purification unit 20. Increasing the pressure in the distillative separation unit (i.e., the distillation column) increases the flow rate of the light inert gas depleted intermediate stream. Reducing the pressure in the distillative separation unit (i.e., the distillation column) reduces the flow rate of the light inert gas depleted intermediate stream.
The source of the second gas may be a first outlet of a purification unit (20), wherein the apparatus further comprises a heat exchanger 40 in signal communication with the controller 80. The heat exchanger 40 may be used to control the temperature in the purification unit. The controller 80 may be used to control the flow rate of the light inert gas from the second gas source 17 to the second inlet of the gas mixer (60) by adjusting the heat load of the heat exchanger 40. Increasing the heat (temperature) from the heat exchanger increases the temperature in the distillation column, which increases the flow rate of the light inert gas in the light inert gas depleted intermediate stream. Reducing the heat (temperature) from the heat exchanger reduces the temperature in the distillation column, which reduces the flow rate of the light inert gas in the light inert gas depleted intermediate stream.
The second gas source may be a first outlet of the purification unit 20, wherein the purification unit 20 comprises one or more apertures operable to control the reflux ratio in said purification unit 20. The controller 80 may be used to control the flow rate of the light inert gas from the second gas source 17 to the second inlet of the gas mixer 60 by adjusting the reflux ratio in the purification unit 20. The "reflux ratio" is defined as the molar flow rate of reflux, which is the liquid stream flowing to the top stage of the distillation column divided by the molar flow rate of vapor or overhead product (i.e., distillate withdrawn from the second outlet). Increasing the reflux ratio increases the flow rate of the light inert gas in the light inert gas depleted intermediate stream. Reducing the reflux ratio reduces the flow rate of the light inert gas in the light inert gas depleted intermediate stream.
The second gas source can be a first outlet of purification unit 20, wherein purification unit 20 includes one or more apertures operable to control a distillate-to-feed ratio in purification unit 20. Controller 80 may be used to control the flow rate of light inert gas from second gas source 17 to the second inlet of gas mixer 60 by adjusting the distillate to feed ratio in purification unit 20. The "distillate to feed ratio" is defined as the molar flow rate of the vapor or overhead product from the distillation column (i.e., the distillate withdrawn from the second outlet), divided by the molar flow rate of the feed to the distillation column. Increasing the distillate to feed ratio decreases the flow rate of the light inert gas in the light inert gas depleted intermediate stream. Decreasing the distillate to feed ratio increases the flow rate of the light inert gas in the light inert gas depleted intermediate stream.
The second gas source may be a first outlet of the purification unit (20), wherein the purification unit 20 comprises one or more apertures operable to control the boiling ratio in the purification unit 20. The controller 80 can be used to control the flow rate of the light inert gas from the second gas source 17 to the second inlet of the gas mixer 60 by adjusting the boiling to feed ratio in the purification unit 20. The "boiling ratio" is defined as the molar flow rate of boiling, which is the vapor flow rate to the bottom stage of the distillation column divided by the molar flow rate of liquid or bottom product (i.e., the bottom stream withdrawn from the first outlet). Increasing the boiling ratio decreases the flow rate of the light inert gas in the light inert gas depleted intermediate stream. Decreasing the boiling ratio increases the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23.
The method includes separating the combined gas stream 12 in an adsorptive separation unit 10 to produce a light inert gas rich intermediate stream 13 and a tail gas stream 51. The adsorption separation unit 10 is an adsorption separation unit.
The cycle time of the adsorption cycle can be set to provide a light inert gas enriched intermediate stream 13 having a volume average ("mixing cup" average) light inert gas concentration of 40 mole% to 90 mole% over the set cycle time. In contrast to conventional operation, the cycle time of the process of the present invention is extended to provide a lower volume average light inert gas concentration for the light inert gas-enriched intermediate stream 13 exiting the adsorptive separation unit 10. Operating the adsorption separation unit 10 with longer cycle times increases the recovery of light inert gases. Due to the low concentration of light inert gases in the feed gas, high recovery is required to be commercially viable.
The process includes separating a purification unit feed gas stream 21 in a purification unit 20 to produce a light inert gas-enriched product stream 25 and a light inert gas-depleted intermediate stream 23. Purification unit feed gas stream 21 comprises light inert gas-enriched intermediate stream 13 from adsorptive separation unit 10. The purification unit 20 may be a membrane type separation unit, an adsorption type separation unit, or a distillation type separation unit.
In the present process, the flow rate of the light inert gas in the second gas stream 17 is controlled in response to a measurement of the light inert gas content in at least one of the feed gas stream 11, the combined gas stream 12, or the adsorption vessel feed gas stream 15. The adsorption vessel feed gas stream 15 comprises at least a portion of the combined gas stream 12.
The light inert gas content can be expressed as concentration or relative amount in the stream.
A measure of the light inert gas content can be determined by measurement of the light inert gas content. A measure of the light inert gas content may be expressed as a volume, molar or mass concentration of the light inert gas. A measure of the light inert gas content may be expressed as a volume, mole or mass fraction or percentage of light inert gas in the mixture.
A measure of the light inert gas content in the adsorptive separation unit feed gas stream 15 may be the concentration of light inert gas in the feed gas stream 11.
The flow rate of the light inert gas in the stream can be expressed as a volumetric, molar or mass flow rate.
For example, if the feed concentration of helium in stream 11 is reduced from 2.0% to 0.5% over time, which is common in natural gas, the helium product purity of adsorption unit 10 will be reduced from 88% to 67%. This reduction in product purity is due to the limitation of keeping the adsorption unit recovered to maximize helium production. However, this reduction in helium product purity may result in a reduction in the purity of the inert-rich gas from the purification unit, as it may not operate efficiently at lower purification unit helium concentrations/purities.
In addition, recycling a higher molar flow rate of light inert gas from purification unit 20 to the feed to adsorptive separation unit 10 increases the recovery of the unit. This effectively increases the overall recovery of the system, since the adsorption type unit 10 is the only significant source of helium loss.
The process may be characterized by
Ratio of light inert gas molar flow rates
And may be less than or equal to 16.
Above 16, a significant amount of the light inert gas is recycled to the adsorptive separation unit 10 and at this point the benefit of recovering the light inert gas is exacerbated and there is no further practical enhancement of the adsorptive separation unit 10.
Allie (US8,268,047) provides an example for helium purification where two VPSAs are in series with a first outlet stream returned to the adsorptive separation unit. From this example, the ratio of the inert gas (helium) flow from the purification unit to the inert gas flow in the feed
The calculation was 0.528. In US5,080,694 to Knoblauch et al, an arrangement of unit operations with recirculation similar to Allie is again used for helium purging. According to the values in Table 5 in the example provided, of Knoblauch
The calculation was 0.222. D' Amico et al (US5,542,966) again used the same arrangement as Allie and Knoblauch et al for helium purging. The values provided in the D' Amico example yield values of 0.408
A ratio. Finally, Choe et al (US4,717,407) used a method of using an initial cryogenic distillation type separation unit in place of an adsorption separation unit, and then using a membrane as a purification unit with the first outlet stream being returned to the cryogenic distillation type separation unit. In a second example of helium purging using the values in Table 4, of Choe
Calculated value was 0.077.
If the light inert gas content is less than the desired lower limit, the flow rate of the light inert gas in the second gas stream 17 may be increased.
If the light inert gas content is greater than the desired upper limit, the flow rate of the light inert gas in the second gas stream 17 may be reduced.
A desired lower limit for the light inert gas content of the combined gas stream 12 may correspond to a light inert gas mole fraction selected from 0.1 mole% to 0.5 mole%. A desired upper limit for the light inert gas content of the combined gas stream 12 may correspond to a light inert gas mole fraction selected from 1.0 mole% to 2 mole%.
The second gas stream 17 can comprise a light inert gas depleted intermediate stream 23 from the purification unit 20. The light inert gas depleted intermediate stream 23 may be compressed in compressor 45. The flow rate of the light inert gas in second stream 17 can be increased or decreased by controlling the operating conditions of purge unit 20 in response to the measurement of the light inert gas content.
The molar flow rate F of light inert gas in the light inert gas depleted intermediate stream 23 can be increased or decreased2, inert propertyIn order to keep the mole fraction of light inert gas in the combined gas stream 12 relatively constant in order to maintain operation within the desired light inert gas recovery range.
The second gas stream 17 can further include a portion 28 of the light inert gas-enriched product stream 25. The flow rate of the light inert gas in the second gas stream 17 can be increased by increasing the flow rate of the portion 28 of the light inert gas-enriched stream 25 and the flow rate of the light inert gas in the second gas stream 17 can be decreased by decreasing the flow rate of the portion 28 of the light inert gas-enriched product stream 25.
In the method, the purification unit may be a membrane separation unit. The membrane separation unit separates the feed stream into a non-permeate stream and a permeate stream. The non-permeate stream is a light inert gas depleted intermediate stream 23. The permeate stream is the light inert gas-enriched product stream 25.
Controlling the operating conditions of the membrane separation unit can include increasing the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23 by decreasing the pressure differential between the membrane separation unit feed gas stream and the light inert gas-enriched product stream. Controlling the operating conditions of the membrane separation unit can include reducing the flow rate of the light inert gas in the light inert gas depleted intermediate stream by increasing the pressure differential between the membrane separation unit feed gas stream and the light inert gas-enriched product stream.
The membrane separation unit may comprise a plurality of membrane modules. Controlling the operating conditions of the membrane separation unit can include increasing the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23 by reducing the number of membrane modules in operation. Controlling the operating conditions of the membrane separation unit can include reducing the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23 by increasing the number of membrane modules in operation.
As mentioned above, the apparatus may include a heat exchanger 40. The operating conditions of the membrane separation unit 20 can be controlled by increasing or decreasing the temperature of the membrane separation unit feed gas stream 21 in the heat exchanger.
Controlling the operating conditions of the membrane separation unit may include increasing the temperature of the membrane separation unit feed gas stream 21 to reduce the flow rate F of light inert gas in the light inert gas depleted intermediate stream 232, inert property. Controlling the operating conditions of the membrane separation unit can include reducing the temperature of the membrane separation unit feed gas stream 21 to increase light inertsFlow rate F of light inert gas in sex gas depleted intermediate stream 232, inert property。
In this method, the purification unit 20 may be an adsorption type separation unit. The adsorptive separation unit separates the feed stream into a tail gas stream and a product stream. The tail gas stream is the light inert gas depleted intermediate stream 23. The product stream is a light inert gas-enriched product stream 25.
The adsorptive separation unit may be operated under an adsorption cycle having a cycle time. Controlling the operating conditions of purification unit 20 can include increasing the cycle time of purification unit 20 to decrease the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23 and/or decreasing the cycle time of purification unit 20 to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23. As cycle times increase, the capacity of the production step for more readily adsorbable species increases due to the increased efficiency of removing more adsorbable species over a longer off-gas generation step time. By increasing the capacity of the more adsorbable species, less of the less adsorbable species (light inert gas) required is captured and lost in the off-gas producing step.
The adsorptive separation unit may have a feed gas header and controlling the operating conditions of purification unit 20 may comprise increasing the pressure of purification unit feed gas stream 21 in the feed gas header of purification unit 20 to decrease the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23 and/or decreasing the pressure of purification unit feed gas stream 21 in the feed gas header of purification unit 20 to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23. As the feed pressure increases, the capacity of the adsorbent for more readily adsorbable species in the production step increases as the efficiency of the adsorbent to adsorb more adsorbable species at higher pressures increases. By increasing the capacity of the more adsorbable species, less of the less adsorbable species (light inert gas) required is captured and lost in the off-gas producing step.
The adsorptive separation unit may have an off-gas header and controlling the operating conditions of the purification unit 20 may comprise increasing the pressure of the light inert gas depleted intermediate stream 23 in the off-gas header of the purification unit 20 to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23 and/or decreasing the pressure of the light inert gas depleted intermediate stream 23 in the off-gas header of the purification unit 20 to decrease the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23. As the pressure of the light inert gas depleted intermediate stream 23 increases, the capacity during the ore adsorbable species production step decreases as the amount of more adsorbable species removed in the off-gas generating step is less. By reducing the capacity of the more adsorbable species, more of the desired less adsorbable species (light inert gas) is captured and lost in the off-gas generating step.
The adsorptive separation unit may be operated under an adsorption cycle comprising a blowdown step having a target pressure at the end of the blowdown step, wherein a blowdown gas stream is formed during the blowdown step. The blowdown gas may be compressed to form a rinse gas stream and/or the blowdown gas may be passed to an exhaust header. Controlling the operating conditions of the purification unit 20 can include increasing the target pressure at the end of the blowdown step to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream 23, and/or decreasing the target pressure at the end of the blowdown step to decrease the flow rate of light inert gas in the light inert gas depleted intermediate stream 23. For the case where the blowdown gas is compressed to form a purge gas stream, increasing the target pressure at the end of the blowdown step results in less light inert gas being removed by the rinse step, captured and returned to the adsorbent bed during the production step. Thus, more light inert gas remains in the bed for the subsequent steps of generating the off-gas (evacuation and/or purging), which therefore increases the amount of light inert gas in the inert gas depleted stream.
The adsorptive separation unit may comprise a plurality of adsorbent beds and operate in a plurality of adsorption cycles, each adsorption cycle comprising a feed step. Controlling the operating conditions of purification unit 20 can include changing to adsorption cycles with fewer adsorbent beds simultaneously during the feed step to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23, and/or changing to adsorption cycles with more adsorbent beds simultaneously during the feed step to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23. As the number of simultaneous adsorbent beds in the feed step decreases, the capacity of the more readily adsorbed species during the production step decreases due to the decrease in the volume of adsorbent available in the feed/production step. By reducing the capacity for more adsorbable species, more of the desired less adsorbable species (light inert gas) is captured and lost in the off-gas generating step.
The adsorptive separation unit may comprise a plurality of adsorbent beds and operate in a plurality of adsorption cycles, some of which include a pressure equalization step. Controlling the operating conditions of the purification unit 20 may include changing to adsorption cycles with fewer or no pressure equalization steps to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23, and/or changing to adsorption cycles with a greater number of pressure equalization steps to decrease the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23. As the amount of pressure equalization is reduced, the capacity for more adsorbable species during the production step is reduced, as the efficiency of removing more adsorbable species in the pressure equalization step is reduced. By reducing the capacity of the more adsorbable species, more of the desired less adsorbable species (light inert gas) is captured and lost in the off-gas generating step.
In this process, the purification unit 20 may be a distillation-type separation unit. The distillative separation unit separates the feed stream into a bottoms stream and an overhead or distillate stream. The bottom stream is the light inert gas depleted intermediate stream 23. The overhead or distillate stream is the light inert gas-enriched product stream 25.
The distillative separation unit can be operated at an operating pressure. Controlling the operating conditions of purification unit 20 can include reducing the operating pressure of purification unit 20 to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23 and/or increasing the operating pressure of purification unit 20 to decrease the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23. As the operating pressure increases, the solubility of the light inert gas in the bottom stream increases, which increases the flow rate of the light inert gas out of the intermediate stream.
The distillative separation unit can be operated at an operating temperature. Controlling the operating conditions of purification unit 20 can include reducing the operating temperature of purification unit 20 to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23 and/or increasing the operating temperature of purification unit 20 to reduce the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23. As the temperature increases, the solubility of the light inert gas in the bottom stream increases, which increases the flow rate of the light inert gas depleted intermediate stream.
The distillative separation unit can be operated at a reflux ratio. Controlling the operating conditions of purification unit 20 may include increasing the reflux ratio of purification unit 20 to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23 and/or decreasing the reflux ratio of purification unit 20 to decrease the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23. As the reflux ratio increases, the amount of reflux increases relative to the overhead or distillate flow rate, wherein the lighter inert gas is "scrubbed" into a liquid solution in the distillative separation unit and thus into the bottoms stream, thereby increasing the light inert gas depletion intermediate stream.
The distillative separation unit can be operated at a distillate to feed ratio. Controlling the operating conditions of purification unit 20 can include increasing the distillate-to-feed ratio of purification unit 20 to decrease the flow rate of light inert gas in the light inert gas depleted intermediate stream 23, and/or decreasing the distillate-to-feed ratio of purification unit 20 to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream 23. As the distillate to feed ratio increases, the distillate flow rate increases relative to the feed flow rate, which reduces the amount/quantity of light inert gas in the distillative separation unit, thereby reducing the bottoms stream, thereby reducing the light inert gas depleted intermediate stream.
The distillative separation unit can be operated at a boiling ratio. Controlling the operating conditions of purification unit 20 can include increasing the boiling ratio of purification unit 20 to decrease the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23, and/or decreasing the boiling ratio of purification unit 20 to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream 23. As the boiling ratio increases, the amount of steam flowing to the bottoms increases relative to the bottoms flow, vaporizing light inert gas from the bottoms stream, thereby reducing the light inert gas from depleting the intermediate stream.
The term "reflux ratio" is a standard term in the art of distillation and is the ratio of reflux flow rate to overhead or distillate flow rate. The term "distillate to feed ratio" is a standard term in the art of distillation and is the ratio of the distillate flow rate to the feed flow rate. The term "boiling ratio" is a standard term in the art of distillation and is the ratio of boiling or steam to bottom stage flow rate to bottom flow rate.
Any desired pretreatment of the gaseous feed mixture to various separation units, or post-treatment of any product stream, as needed or desired, may be used with the process and apparatus. For example, depending on the choice of adsorbent used, a pretreatment to remove certain components from feed gas stream 11 may be required, which may adversely affect the adsorbent or the process. Similarly, there may be a component in the final helium product, namely the helium-rich permeate stream 25, which may be undesirable in the subsequent use of the product stream and must be removed in a post-processing operation prior to its use.
The embodiment of the invention shown in figure 8 first separates the feed gas stream 11 in a feed membrane separation unit 85. The feed membrane separation unit may be any separation unit that uses a membrane to separate a feed stream into two streams, each resulting stream having a different concentration of a species. The membrane may be a semi-permeable membrane or a selectively permeable membrane. Membranes separate gas mixtures by allowing certain gaseous species to pass through the membrane by diffusion, facilitated diffusion, passive transport, and/or active transport.
The membrane separation unit may be any membrane device that has a certain selectivity for separating the light inert gas from the other components in the feed while maintaining a pressure differential across the membrane. When the light inert gas is helium, the helium permeability through the membrane is typically greater than the helium permeability of the other components present in the membrane feed. Thus, the helium concentration in the non-permeate stream from the membrane separation unit is less than the concentration in the feed stream to the membrane separation unit. In fig. 8, the feed gas 11 is separated into a permeate stream 41 enriched in light inert gas relative to the feed and a non-permeate stream 42 depleted in light inert gas relative to the feed.
The feed membrane separation unit 85 may consist of a single membrane unit or, alternatively, be constructed and operated from several membrane units to achieve separation in the most efficient manner, e.g., cascaded membranes with internal recycle streams between the various stages of the membrane unit. Typically, membrane devices are manufactured in modules, each module having certain semi-permeable membrane regions for permeation. The membrane material may also be selected from the list of materials discussed for the membrane-type separation unit, or any other material having a faster permeation rate for certain compounds (e.g., helium) and a slower permeation rate for certain compounds (e.g., methane).
The permeate stream 41 is combined with the second gas stream 17, and the second gas stream 17 is recycled from downstream processing steps to form the combined gas stream 12. The combined gas may then enter compressor 55 before being fed to the adsorptive separation unit 10, if desired. The permeate stream 41 may be combined with the second gas stream 17 in a gas mixer 60. As shown in fig. 1, the combined gas stream 12 may be compressed in a compressor 55 to feed an adsorptive separation unit 10, which separation unit 10 separates the stream into a light inert gas rich intermediate stream 13 and a tail gas stream 51 lean in light inert gas relative to the combined gas stream 12, if desired.
If desired, the light inert gas enriched intermediate stream 13 can be heated or cooled in heat exchanger 40, pressurized in compressor 35, or depressurized in adjustable orifice 32 to form purification unit feed gas stream 21. Purification unit 20 separates purification unit feed gas stream 21 into a light inert gas-enriched product stream 25 and a light inert gas-depleted intermediate stream 23.
The second gas stream 17 can comprise a light inert gas depleted intermediate stream 23, which can be compressed in compressor 45 to match the pressure of permeate stream 41, if desired. The second gas stream 17 can further include a portion 28 of the light inert gas-enriched product stream 25. Portion 28 may be a separate or separate portion of stream 25.
In the present process, the flow rate of the light inert gas in the second gas stream 17 is controlled in response to a measurement of the light inert gas content in at least one of the feed gas stream 11, the permeate stream 41, the combined gas stream 12, or the adsorption vessel feed gas stream 15. The adsorption vessel feed gas stream 15 comprises at least a portion of the combined gas stream 12.
Because the feed membrane 85 is enriched in the light inert gas content of the permeate stream 41 compared to the feed gas 11, the desired upper limit for the light inert gas mole fraction of the combined gas stream 12 will be higher than in the embodiment shown in fig. 1. In the embodiment shown in fig. 8, a desirable upper limit for the light inert gas fraction of the combined gas stream 12 may be from 5 mole% to 20 mole%.
The present process can include the combination of tail gas stream 51 and non-permeate stream 42 to form light inert gas-lean product stream 14. For example, if feed gas 11 is rich in methane, stream 14 may be returned to a pipeline or combusted to obtain heat and/or power. If the pressure of the tail gas stream 51 is lower than the non-permeate 42, the stream 51 may be compressed in a tail gas compressor 90 to form a compressed tail gas stream 53. The compressed tail gas stream 53 can be combined with the non-permeate gas stream 42 in a gas mixer 95 to form the light inert gas-lean product stream 14.
Examples
Example 1
A multi-bed adsorption pilot plant/experimental setup was set up to collect light inert gas recovery data for the adsorption separation unit. The apparatus consisted of 5 adsorbent beds, each having an internal diameter of 2.21 cm (0.87 inch) and a length of 3.05 m (10 ft). The adsorption cycle used is shown in FIG. 2, which is a 5-bed vacuum pressure swing adsorption (VSA) with a rinse step (described above). The bed was packed with activated carbon adsorbent and cycle times varied between 30 seconds, 60 seconds and 120 seconds. The feed composition of the unit varied from 0.35 thick mol% He to 4 mol% He, with nitrogen, methane and carbon dioxide making up the balance of the feed gas. The feed pressure was varied between 345kPa (absolute) and 1029kPa (absolute) and the feed temperature was 21.1 c (70F). An optional surge tank 30 is included in the experimental setup and product purity is measured at the outlet of this tank, which is equivalent to the purification unit inlet stream 21 in fig. 1.
In the first experiment, different amounts/concentrations of helium were fed to the experimental equipment and the total helium recovery was measured. The curve in FIG. 4 entitled "AP Experimental System" shows the results for varying the feed helium mole percent for the adsorption unit, with a helium product purity of 70 mole percent and a rinse to feed ratio of 1: 1 for all data points on the curve. As can be seen in fig. 4, the right-hand side of fig. 4 (higher helium feed gas concentration) operation is more favorable for overall system helium recovery. In fact, the feed gas helium concentration in stream 11 of FIG. 1 varies and decreases over time.
Thus, maintaining the helium concentration of the adsorption unit brings value and benefits. Higher helium concentrations in the adsorption unit can be achieved by circulating helium from the second downstream separation unit. However, the recovery of helium from the second downstream separation unit is counterintuitive, since the (first) adsorptive separation unit is the only source of helium loss, resulting in a lower helium recovery. However, if helium recovery from the (first) adsorptive separation unit can be improved to the point where the benefit of the additional helium feed concentration outweighs the loss of helium, this would provide a non-obvious benefit.
In another set of experiments, the experimental system was run at a different second volume V2And (5) operating. FIG. 5 shows experimental results for helium recovery for an adsorption type system of the present invention, which varies with the second volume. The data in FIG. 5 are for 2 mole% helium in the feed and a 1: 1 rinse to feed ratio. The rinse to feed ratio is a measure of the molar flow rate of gas withdrawn from the bed during the rinse step (stream 18 in fig. 1) divided by the molar flow rate of the combined gas (stream 12 in fig. 1) gas fed into the bed in the feed step. By monitoring and controlling pressure in the bed at the end of the blowdown stepThe ratio is made. In the experimental system, this was done by adding isolation valves at the feed and product ends of the column/bed, effectively reducing the second volume. As is clear from fig. 5, reducing the second volume will increase the helium recovery.
According to experimental results, another unexpected benefit of maintaining helium concentration in the combined gas (stream 12 in fig. 1) was observed, which is shown in fig. 6. As the helium concentration in the combined gas (stream 12 in fig. 1) decreases, the helium product purity from the adsorption unit (stream 21 in fig. 1) also decreases. This variation in product purity of the second unit feed stream 21 can result in difficulty in controlling the purification unit, since the feed concentration is known to vary and decline over time. In addition, these variations can lead to a reduction in the light inert gas-enriched product stream 25 due to the limited/practical design basis of the purification unit. The reduction in the light inert gas-enriched product stream 25 below the desired purity of the light inert gas may force the plant to drop significantly or may shut down.
Example 2
The object of the present invention is to simultaneously handle light inert gas recovery and simultaneously handle varying and low concentrations of light inert gas in the feed by recycling the second stream rich in light inert gas to enrich the light inert gas content of the feed to the adsorptive separation unit. According to the findings of the experimental system, efforts have been intentionally made to maximize helium recovery in the prior art by reducing the second volume of the adsorption unit. The curve in FIG. 4 entitled "header Change" illustrates the effect of simulation modeling by reducing the second volume of a typical commercial system by 50% by rearranging and/or minimizing the conduit volume.
The curve in fig. 4 entitled "isolation valve" employs isolation switch valves that are in fluid communication with the beds at the feed and product ends of the adsorbent beds. This significantly reduces the second volume compared to "header changes" and "commercial systems", thereby improving adsorption and helium recovery throughout the system. The isolation valves on the product manifold are open during production (P), flushing (R), and Product Pressurization (PP), but closed during Blowdown (BD) and evac (e). The isolation on the feed header is closed during Product Pressurization (PP) and opened during all other adsorption steps to prevent gas with high helium concentration from entering the second volume at the feed end of the bed.
By reducing the second volume through header variation or isolation valves, helium recovery at all combined gas stream 12 concentrations is significantly improved over the prior art and enables the present invention to achieve higher recoveries (0.1% to 4%) over the entire target helium concentration range, as shown in FIG. 4.
Example 3
Greater benefits may be seen where the helium content of the incoming feed gas stream 11 drops by 4% to 0.5% over time. The prior art in this example is US8268047, a dual VPSA for helium recovery. As shown in fig. 6, this change in helium content of feed gas stream 11 will result in a decrease in helium purity of the adsorption unit rich gas stream 13.
Because of the low purity entering the second stage inlet, the prior art must have a 'short cycle' (well known to those skilled in the art of adsorption) final purification stage to maintain the final helium purity given the fixed system that has been run. This inherently increases the second flow helium (F)2, inert property) This results in an increase in helium loss as shown by the curve labeled "prior art" in fig. 7.
In the present invention, the recovery of the adsorption separation unit is implicitly higher due to the minimization of the second volume in the adsorption separation unit, which enables a positive increase in the feed content as it decreases
This results in a significant improvement in helium recovery compared to the prior art, as the feed content is reduced, as shown in FIG. 7.
Example 4
The present invention may be used to extract and purify helium from a Boil Off Gas (BOG) fuel stream from a storage tank in a Liquefied Natural Gas (LNG) export facility. BOG is ideal for treatment using the present invention because the concentration of contaminants, including water vapor, acid gases such as CO, is very low2And H2S, and/or heavy hydrocarbons inUpstream of the LNG facility is removed. Furthermore, BOG has a helium content concentration higher than the typical level found in natural gas in LNG processes. This example describes the extraction of helium from a BOG stream, which has a high degree of variability in flow rate and helium concentration due to changes in the operating mode of an LNG facility. Many LNG facilities have multiple trains in parallel. This allows the number of trains in operation, the number of LNG storage tanks in operation and the number of vessels being loaded to be manipulated to create different modes of operation. All of these factors affect the BOG flow rate and the concentration of helium contained. Once BOG leaves the LNG storage tank, it is typically compressed by the LNG facility and burned in a gas turbine or recycled to the front of the LNG facility. In this example, the compressed BOG stream enters the process shown in fig. 8 as feed gas 11. The light inert gas-lean product stream 14 can be returned to the BOG system of the LNG facility with minimal pressure loss. The present invention does not actually interact with the upstream processes at the LNG facility, which reduces any risk of adversely affecting larger LNG facilities in the present invention.
Tables 1 and 2 show exemplary stream conditions for extracting helium from BOG from an LNG facility in two modes of operation. Table 1 shows the "normal operation" mode, defined as no loading vessel, which is the most common operation mode for LNG facilities. Table 2 details the "ship loading" mode, defined as the case of loading one or more ships while maintaining the LNG liquefaction train in operation.
The BOG feed stream 11 during the ship loading mode has a higher flow rate and a lower helium concentration than during the normal operating mode. Due to the heat exchange cooling duty and flow rate limitations in the distillation column, it would be extremely difficult to design an integrated cryogenic distillation system for both modes. In contrast, the present invention is well suited to feed streams having widely varying flow rates. Given a constant feed pressure, the feed membrane separation unit 85 maintains a steady flow rate in the permeate 41 over a wide range of inlet flow rates, which is achieved by a constant active zone in the feed membrane separation unit 85. This effectively isolates the downstream unit operations 10 and 20 from upstream variations in the flow rate of the feed stream 11. The change in helium concentration in BOG feed stream 11 propagates to permeate stream 41, but then, by varying the operation of purification unit 20 to control the molar flow rate of helium in second gas stream 17, the helium concentration in combined gas stream 12 can be controlled to maintain stable operation of the adsorption unit. Although the difference in the molar flow rates of the feed gas 11 was 2.7 times, the combined stream 12 supplied to the adsorption separation unit 10 varied by less than 1%. Those skilled in the art will appreciate that the design and operation of both the adsorption equipment and the compressor downstream of the feed membrane unit 85 are significantly simplified when the flow rate is kept approximately constant. In a typical operation, if the molar flow rate of the feed gas to the adsorption units varies by a factor of 2.7, multiple columns of adsorption units need to be used. Therefore, the present invention can provide a stable flow rate to the adsorption separation unit 10, which allows stable operation without additional equipment cost.
Table 1: normal operation mode
Table 2: ship loading mode
| Flow of | 11 | 12 | 13 | 14 | 17 | 25 | |
| Pressure of | kPa_a | 5000 | 700 | 650 | 4980 | 700 | 500 |
| Temperature of | ℃ | 40 | 38 | 40 | 38 | 40 | 38 |
| Flow rate of flow | kmol/hr | 3400 | 322 | 41 | 3386 | 27 | 14 |
| Composition of | |||||||
| Methane (C1) | mol％ | 88.5 | 77.5 | 0.0 | 90.6 | 0.0 | 0.0 |
| Nitrogen (N2) | mol％ | 11.0 | 15.0 | 30.0 | 9.2 | 60.0 | 1.0 |
| Helium (He) | mol％ | 0.55 | 7.5 | 70.0 | 0.2 | 40.0 | 99.0 |
Example 5
The helium concentration in the raw natural gas may vary from about 200 to about 600ppm and still facilitate the application of the present invention to recover helium using a process corresponding to figure 8. Process economics with helium levels below about 200ppm in the original natural gas may not be attractive, and helium levels above about 600ppm may justify integrating helium recovery into the LNG process, which would leave no helium in the BOG for recovery.
While example 4 considers the case of 200ppm helium in the raw natural gas entering the LNG process, example 5 uses the case of 600ppm helium in the raw natural gas. As shown in table 3, the BOG constituting stream 11 contains 3.9% helium and the combined gas stream 12 contains 17.5% helium. Note that the helium concentration in the light inert gas enriched intermediate 13 and the second gas stream 17 is constant. Examples 4 and 5 illustrate the most common helium concentration range contemplated in the application of the present invention as shown in fig. 8.
Table 3: high helium natural gas
| Flow of | 11 | 12 | 13 | 14 | 17 | 25 | |
| Pressure of | kPa_a | 5000 | 700 | 650 | 4980 | 700 | 500 |
| Temperature of | ℃ | 40 | 38 | 40 | 38 | 40 | 38 |
| Flow rate of flow | kmol/hr | 1300 | 403 | 107 | 1250 | 57 | 50 |
| Composition of | |||||||
| Methane (C1) | mol％ | 85.6 | 64.2 | 0.0 | 88.9 | 0.0 | 0.0 |
| Nitrogen (N2) | mol％ | 10.5 | 18.3 | 30.0 | 10.9 | 59.9 | 1.0 |
| Helium (He) | mol％ | 3.9 | 17.5 | 70.0 | 0.2 | 40.1 | 99.0 |
Claims (28)
1. An apparatus for producing a light inert gas-enriched product stream from a feed gas, the feed gas comprising a light inert gas and at least one other gaseous component, the light inert gas selected from the group consisting of helium and neon, the apparatus comprising:
a feed membrane separation unit having an inlet for receiving a feed gas stream, a permeate outlet, and a non-permeate outlet;
an adsorptive separation unit, wherein the adsorptive separation unit comprises:
a plurality of vessels, each vessel comprising a bed of adsorbent;
a feed gas header in selective fluid communication with each of the plurality of vessels;
a product gas header in selective fluid communication with each of the plurality of vessels;
an off-gas header in selective fluid communication with each of the plurality of vessels;
a process gas delivery line operatively connecting the plurality of vessels to the feed gas header, the product gas header, and the off-gas header;
each of the plurality of vessels having a process gas delivery line associated therewith;
a plurality of valves in the process gas delivery line, including a plurality of valves adjacent to and associated with each respective container;
wherein the adsorption separation unit has a central volume Vc of the process gas transfer line associated with each respective vessel;
wherein the central volume of each respective container is the sum of:
(i) a volume contained in a process gas delivery line associated with a respective vessel connecting the respective vessel to each valve in the vicinity of the respective vessel,
(ii) all dead end volumes, if any, are connected to the respective containers at junctions, and
(iii) all dead-end volumes, if any, are connected at junctions to any process gas delivery lines associated with the respective vessels that connect the respective vessels to any valves adjacent to the respective vessels;
wherein the central volume of each respective container comprises a second volume V2, wherein the second volume is the sum of:
(i) all volumes of dead end volume, if any, are connected to the respective container;
(ii) all volumes of dead end volume, if any, are connected at a junction to any process gas delivery line associated with a respective vessel, the gas delivery line connecting the respective vessel to any valve adjacent to the respective vessel; and
(iii) a volume of any process gas delivery line, if any, having a first end terminating in a valve adjacent the respective vessel, the valve configured to allow process gas to be delivered to the off-gas header when open, and having a second end terminating at a junction in any other associated process gas delivery line connecting the respective vessel to any other valve adjacent the respective vessel;
wherein the second volume V2 is less than 5% of the central volume Vc of each container; and
a conduit system for conveying a permeate stream from the permeate outlet to a feed gas header of the adsorptive separation unit.
2. The apparatus of claim 1, further comprising:
a purification unit having an inlet in fluid communication with the product gas header of the adsorptive separation unit, a first outlet, and a second outlet;
wherein the conduit system comprises a gas mixer having a first inlet for receiving the permeate stream, a second inlet in fluid communication with a second gas source having a higher concentration of light inert gas than the permeate gas, and an outlet in fluid communication with the combined gases, wherein the feed gas header of the adsorptive separation unit is in downstream fluid communication with the outlet of the gas mixer;
a sensor in at least one of: (i) a feed gas line supplying an inlet of the feed membrane separation unit; (ii) a permeate stream line connecting the permeate outlet of the feed membrane separation unit to the first inlet of the gas mixer; (iii) a combined gas flow line connecting the outlet of the gas mixer to the feed gas header of the adsorption separation unit; and (iv) a feed gas header; and
a controller in signal communication with the sensor, the controller operable to control a flow rate of light inert gas from the second gas source to the second inlet of the gas mixer in response to a signal from the sensor.
3. The apparatus of claim 2, wherein the second gas source comprises a first outlet of the purge unit.
4. The apparatus of claim 2, wherein the second gas source comprises a second outlet of the purification unit.
5. The apparatus of claim 2, wherein the second gas source comprises a process gas delivery line operatively connecting the product gas header to an inlet of the purification unit.
6. The apparatus of claim 2, wherein the gas mixer has a third inlet in fluid communication with the second outlet of the purification unit.
7. The apparatus of claim 2 wherein the gas mixer has a third inlet in fluid communication with a process gas delivery line operatively connecting the product gas header of the adsorptive separation unit to the inlet of the purification unit.
8. The apparatus of claim 2, wherein the purification unit is a membrane separation unit,
wherein the second gas source comprises a first outlet of the purification unit; and
wherein at least one of:
(a) the purification unit comprising one or more adjustable orifices in signal communication with the controller, the one or more adjustable orifices operative to control pressure in the purification unit; and
the controller is operable to control a flow rate of the light inert gas from the second gas source to the second inlet of the gas mixer by adjusting the one or more adjustable orifices;
(b) the membrane separation unit comprises a plurality of membrane modules and one or more control valves controlling portions of the membrane modules in operation, the one or more control valves in signal communication with the controller; and
the controller is operable to control the flow rate of light inert gas from the second gas source to the second inlet of the gas mixer by adjusting the portion of the membrane module that is in operation; or
(c) The apparatus includes a heat exchanger operable to control a temperature in the purification unit, the heat exchanger in signal communication with the controller; and
the controller is operable to control the flow rate of light inert gas from the second gas source to the second inlet of the gas mixer by adjusting the heat load of the heat exchanger.
9. The apparatus of claim 2, wherein the purification unit is an adsorptive separation unit,
wherein at least one of:
(a) the second gas source comprises a first outlet of the purification unit;
the adsorptive separation unit comprises a plurality of vessels each containing a bed of adsorbent and one or more control valves controlling portions of the plurality of vessels in operation, the one or more control valves in signal communication with the controller; and
the controller is operable to control the flow rate of light inert gas from the second gas source to the second inlet of the gas mixer by adjusting the portion of the plurality of vessels in operation;
(b) the second gas source comprises a first outlet of the purification unit;
the purification unit includes a feed gas header,
the purification unit comprises one or more adjustable orifices operative to control pressure in a feed gas header of the purification unit; and
the controller is operable to control the flow rate of light inert gas from the second gas source to the second inlet of the gas mixer by adjusting one or more adjustable orifices operative to control the pressure in the feed gas header of the purification unit;
(c) the second gas source comprises a first outlet of the purification unit;
the purification unit comprises an exhaust gas header pipe,
the purification unit comprising one or more adjustable orifices operative to control pressure in an exhaust header of the purification unit; and
the controller is operable to control the flow rate of light inert gas from the second gas source to the second inlet of the gas mixer by adjusting one or more adjustable orifices operative to control the pressure in the off-gas header of the purification unit; or
(d) The second gas source comprises a second outlet of the purification unit;
the purification unit includes a product gas header,
the purification unit comprises one or more adjustable orifices operative to control pressure in a product gas header of the purification unit; and
the controller is operable to control the flow rate of light inert gas from the second gas source to the second inlet of the gas mixer by adjusting one or more adjustable orifices operative to control the pressure in the product gas header of the purification unit; or
(e) The second gas source comprises a second outlet of the purification unit;
the apparatus includes a heat exchanger operable to control a temperature in the purification unit, the heat exchanger in signal communication with the controller; and
the controller is operable to control the flow rate of light inert gas from the second gas source to the second inlet of the gas mixer by adjusting the heat load of the heat exchanger.
10. The apparatus of claim 9, wherein the purification unit is a rapid cycle adsorption unit.
11. The apparatus of claim 10, wherein the rapid cycle adsorption unit comprises one or more rotary valves.
12. The apparatus of claim 10, wherein the fast cycle adsorption unit comprises a rotor assembly and first and second stator assemblies, wherein:
the rotor assembly is located between the first and second stator assemblies and comprises a plurality of adsorbent beds, each bed having a rotor port at either end of the bed through which gas enters or exits the bed;
the first stator assembly includes at least one feed port, at least one discharge port, and a first stator plate having: at least one feed chute for directing at least one feed gas stream from the feed inlet into any one of the rotor ports aligned with the feed chute; at least one discharge slot for directing a flow of a discharge gas stream from any one of the rotor ports aligned with the discharge slot to the discharge port; and
the second stator assembly includes at least one product port and a second stator plate having: at least one product tank for directing at least one product gas stream to flow between the product port and any one of the rotor ports aligned with the product tank; and at least one purge slot for directing a flow of at least one purge gas stream into any of the rotor ports aligned with the purge slot;
the rotor assembly is rotatable relative to the first and second stator assemblies to change the mode of operation of the respective adsorbent beds by changing the rotor ports aligned with the slots in the first and second stator plates.
13. The apparatus of claim 10, wherein the rapid cycle adsorption unit comprises 6 to 9 beds, each bed comprising a bed of adsorbent.
14. The apparatus of claim 2, wherein the purification unit is a distillation separation unit,
wherein the second gas source comprises a first outlet of the purification unit; and
wherein at least one of:
(a) the purification unit comprising one or more adjustable orifices in signal communication with the controller, the one or more adjustable orifices operative to control pressure in the purification unit; and
the controller is operable to control the flow rate of light inert gas from the second gas source to the second inlet of the gas mixer by adjusting one or more adjustable orifices that operate to control the pressure in the purification unit;
(b) the apparatus includes a heat exchanger operable to control a temperature in the purification unit, the heat exchanger in signal communication with the controller; and
the controller is operable to control the flow rate of light inert gas from the second gas source to the second inlet of the gas mixer by adjusting the heat load of the heat exchanger;
(c) the purification unit comprises one or more orifices operative to control a reflux ratio in the purification unit; and
the controller is operable to control a flow rate of light inert gas from the second gas source to the second inlet of the gas mixer by adjusting a reflux ratio in the purification unit;
(d) the purification unit comprises one or more orifices operative to control a distillate to feed ratio in the purification unit; and
the controller is operable to control a flow rate of light inert gas from the second gas source to the second inlet of the gas mixer by adjusting a distillate to feed ratio in the purification unit; or
(e) The purification unit comprises one or more orifices operative to control a product to feed ratio in the purification unit; and
the controller is operable to control a flow rate of light inert gas from the second gas source to the second inlet of the gas mixer by adjusting a distillate to feed ratio in the purification unit.
15. A process for separating a feed gas stream comprising a light inert gas and at least one other gas component into a light inert gas-enriched product stream and a light inert gas-depleted product stream, the light inert gas being selected from the group consisting of helium and neon, the process comprising:
separating the feed gas stream in a feed membrane separation unit to produce a permeate stream and a non-permeate stream;
combining the permeate stream with a second gas stream having a higher light inert gas content than the permeate stream to form a combined gas stream, the second gas stream having an adjusted flow rate;
separating an adsorptive separation unit feed gas stream in an adsorptive separation unit to produce a light inert gas-enriched intermediate stream and a tail gas stream, wherein the light inert gas-lean product stream comprises at least a portion of the tail gas stream, wherein the adsorptive separation unit feed gas stream comprises at least a portion of a combined gas stream; and
separating a purge unit feed gas stream in a purge unit to produce a light inert gas-enriched product stream and a light inert gas depleted intermediate stream, wherein the purge unit feed gas stream comprises at least a portion of the light inert gas enriched intermediate stream from the adsorptive separation unit;
wherein the flow rate of the light inert gas in the second gas stream is controlled in response to a measure of the light inert gas content in at least one of the feed gas stream, the permeate stream, the combined gas stream, or the adsorptive separation unit feed gas stream.
16. The method of claim 15, wherein the adsorptive separation unit comprises:
a plurality of vessels, each containing a bed of adsorbent;
a feed gas header in selective fluid communication with each of the plurality of vessels;
a product gas header in selective fluid communication with each of the plurality of vessels;
an off-gas header in selective fluid communication with each of the plurality of vessels;
a process gas delivery line operatively connecting the plurality of vessels to the feed gas header, the product gas header, and the off-gas header;
each of the plurality of vessels having a process gas delivery line associated therewith;
a plurality of valves in the process gas delivery line, including a plurality of valves adjacent to and associated with each respective container;
wherein the adsorption separation unit has a central volume Vc of the process gas transfer line associated with each respective vessel;
wherein the central volume of each respective container is the sum of:
(i) a volume contained in a process gas delivery line associated with a respective vessel connecting the respective vessel to each valve in the vicinity of the respective vessel,
(ii) all dead end volumes, if any, are connected to the respective containers at junctions, and
(iii) all dead-end volumes, if any, are connected at junctions to any process gas delivery lines associated with the respective vessels that connect the respective vessels to any valves adjacent to the respective vessels;
wherein the central volume of each respective container comprises a second volume V2, wherein the second volume is the sum of:
(i) all volumes of dead end volume, if any, are connected to the respective container;
(ii) all volumes of dead end volume, if any, are connected at a junction to any process gas delivery line associated with a respective vessel, the gas delivery line connecting the respective vessel to any valve adjacent to the respective vessel; and
(iii) a volume of any process gas delivery line, if any, having a first end terminating in a valve adjacent the respective vessel, the valve configured to allow process gas to be delivered to the off-gas header when open, and having a second end terminating at a junction in any other associated process gas delivery line (102) connecting the respective vessel to any other valve adjacent the respective vessel; and
wherein the second volume V2 is less than 5% of the central volume Vc of each container.
17. The method of claim 15, wherein the permeate gas stream has a total gas molar flow rate F1Wherein the molar flow rate of the light inert gas F1, inertAnd said second gas stream has a total gas molar flow rate F2Wherein the molar flow rate of the light inert gas F2, inert propertyAnd wherein
18. The method of claim 15, wherein
If the light inert gas content is less than the desired lower limit, the flow rate of light inert gas in the second gas stream is increased; and/or if the light inert gas content is greater than a desired upper limit, the flow rate of light inert gas in the second gas stream is reduced.
19. The method of claim 15, wherein the second gas stream comprises a light inert gas depleted intermediate stream, and wherein the flow rate of light inert gas in the second stream is increased or decreased by controlling operating conditions of the purification unit in response to the light inert gas content.
20. The method of claim 19, wherein the purification unit is a membrane-based separation unit comprising a plurality of membrane modules, and wherein controlling the operating conditions of the purification unit comprises at least one of:
(a) reducing the pressure differential between the purification unit feed gas stream and the light inert gas-enriched product stream to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream; and/or
Increasing the pressure differential between the purification unit feed gas stream and the light inert gas-enriched product stream to reduce the flow rate of light inert gas in the light inert gas depleted intermediate stream;
(b) reducing the number of membrane modules in operation to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream; and/or
Increasing the number of membrane modules in operation to reduce the flow rate of the light inert gas in the light inert gas depleted intermediate stream; or
(c) Increasing the temperature of the purification unit feed gas stream to reduce the flow rate of the light inert gas depleted intermediate stream; and/or
Reducing the temperature of the purification unit feed gas stream to increase the flow rate of the light inert gas depleted intermediate stream.
21. The method of claim 19, wherein the purification unit is an adsorptive separation unit, wherein at least one of the following control schemes is employed:
(a) the adsorptive separation unit is operated in an adsorption cycle having a cycle time and controlling the operating conditions of the purification unit comprises:
increasing the cycle time of the purification unit to decrease the flow rate of light inert gas in the light inert gas depleted intermediate stream; and/or
Reducing the cycle time of the purification unit to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream;
(b) the adsorptive separation unit is operated in an adsorption cycle comprising a purge step containing the light inert gas in the light inert gas enriched intermediate stream and controlling the operating conditions of the purification unit comprises:
increasing the flow rate of the purging step to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream; and/or
Reducing the flow rate of the purge step to reduce the flow rate of light inert gas in the light inert gas depleted intermediate stream;
(c) the adsorptive separation unit has a feed gas header and controlling the operating conditions of the purification unit comprises:
increasing the pressure of the purge unit feed gas stream in the purge unit feed gas header to reduce the flow rate of the light inert gas depleted intermediate stream; and/or
Reducing the pressure of the purge unit feed gas stream in the purge unit feed gas header to increase the flow rate of the light inert gas depleted intermediate stream;
(d) the adsorptive separation unit has an off-gas header and controlling the operating conditions of the purification unit comprises:
increasing the pressure of the light inert gas depleted intermediate stream in the off-gas header of the purification unit to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream; and/or
Reducing the pressure of the light inert gas depleted intermediate stream in the off-gas header of the purification unit to reduce the flow rate of light inert gas in the light inert gas depleted intermediate stream;
(e) the adsorptive separation unit is operated in an adsorption cycle comprising a blowdown step having a target pressure for blowdown step end, and controlling the operating conditions of the purification unit comprises:
increasing the target pressure at the end of the blowdown step to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream; and/or
Reducing the target pressure at the end of the blowdown step to reduce the flow rate of light inert gas in the light inert gas depleted intermediate stream;
(f) the adsorptive separation unit comprises a plurality of adsorbent beds and operates in a plurality of adsorption cycles each comprising a feed step, and controlling the operating conditions of the purification unit comprises:
simultaneously changing over the feed step to an adsorption cycle having a lesser number of adsorbent beds to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream; and/or
Simultaneously changing over the feed step to an adsorption cycle having a greater number of adsorbent beds to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream; or
(g) The adsorptive separation unit comprises a plurality of adsorbent beds and is operated in a plurality of adsorption cycles comprising a pressure equalization step, and controlling the operating conditions of the purification unit comprises:
altering the adsorption cycle to have a lesser degree of pressure equalization by using fewer or no pressure equalization steps and/or reducing the total moles of gas delivered in one or more pressure equalization steps to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream; and/or
Changing to an adsorption cycle having a greater degree of pressure equalization by using a greater number of pressure equalization steps and/or increasing the total moles of gas delivered in one or more pressure equalization steps to reduce the flow rate of light inert gas in the light inert gas depleted intermediate stream; or
(h) The adsorptive separation unit is operated in a cycle comprising feed and product repressurization steps, and controlling the operating conditions of the purification unit comprises:
increasing the ratio of feed flow to product flow in the repressurization step to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream; and/or
Reducing the ratio of feed flow to product flow in the repressurization step to reduce the flow rate of the light inert gas depleted intermediate stream; or
(i) The adsorptive separation unit is operated in a cycle comprising a feed temperature and an optimum temperature to maximize working capacity, and controlling the operating conditions of the purification unit comprises:
operating at said feed temperature close to an optimum temperature to reduce the flow rate of light inert gas in said light inert gas depleted intermediate stream; and/or
Operating to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream with the feed temperature further away from the optimum temperature.
22. The method of claim 21, wherein the purification unit is a rapid cycle adsorption unit.
23. The method of claim 22, wherein the rapid cycle adsorption unit comprises one or more rotary valves.
24. The method of claim 22, wherein the first and second portions are selected from the group consisting of,
wherein the fast cycle adsorption unit comprises a rotor assembly and first and second stator assemblies, wherein:
the rotor assembly is located between the first and second stator assemblies and comprises a plurality of adsorbent beds, each bed having a rotor port at either end of the bed through which gas enters or exits the bed;
the first stator assembly includes at least one feed port, at least one discharge port, and a first stator plate having: at least one feed chute for directing at least one feed gas stream from the feed inlet into any one of the rotor ports aligned with the feed chute; at least one discharge slot for directing a flow of a discharge gas stream from any one of the rotor ports aligned with the discharge slot to the discharge port; and
the second stator assembly includes at least one product port and a second stator plate having: at least one product tank for directing at least one product gas stream to flow between the product port and any one of the rotor ports aligned with the product tank; and at least one purge slot for directing a flow of at least one purge gas stream into any of the rotor ports aligned with the at least one purge slot;
the rotor assembly is rotatable relative to the first and second stator assemblies to change the mode of operation of the respective adsorbent beds by changing the rotor ports aligned with the slots in the first and second stator plates.
25. The method of claim 22, wherein the rapid cycle adsorption unit comprises 6 to 9 beds, each bed comprising a bed of adsorbent.
26. The method of claim 19, wherein the purification unit is a distillation separation unit having a reflux ratio and operating at an operating pressure and an operating temperature, wherein controlling the operating conditions of the purification unit comprises at least one of:
(a) reducing the operating pressure of the purification unit to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream; and/or
Increasing the operating pressure of the purification unit to reduce the flow rate of light inert gas in the light inert gas depleted intermediate stream;
(b) increasing the reflux ratio of the purification unit to increase the flow rate of the light inert gas in the light inert gas depleted intermediate stream; and/or
Reducing the reflux ratio of the purification unit to reduce the flow rate of the light inert gas in the light inert gas depleted intermediate stream; or
(c) Reducing the operating temperature of the purification unit to increase the flow rate of light inert gas in the light inert gas depleted intermediate stream; and/or
Increasing the operating temperature of the purification unit to decrease the flow rate of the light inert gas in the light inert gas depleted intermediate stream.
27. The method of claim 15, wherein the second gas stream comprises a portion of the light inert gas-enriched product stream having a flow rate, and the flow rate of the light inert gas in the second gas stream is increased by increasing the flow rate of the portion of the light inert gas-enriched product stream and decreased by decreasing the flow rate of the portion of the light inert gas-enriched product stream.
28. The process of claim 15, wherein the feed gas stream has a molar concentration of light inert gas in the following range: 0.1 mol% of light inert gas to 2.0 mol% of light inert gas.
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| US16/251,594 US10843121B2 (en) | 2017-12-21 | 2019-01-18 | Separation process and apparatus for light noble gas |
| US16/251594 | 2019-01-18 |
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| AU2019202519B2 (en) | 2020-11-05 |
| CN111450667A (en) | 2020-07-28 |
| CA3040413C (en) | 2021-12-14 |
| AU2019202519A1 (en) | 2020-08-06 |
| CA3040413A1 (en) | 2020-07-18 |
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